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Solution reactions of HX molecules (X = SH, Cl, Br) with dinuclear palladium(I) complexes containing… Barnabas, Freddy A. 1989

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e Solution Reactions of H X Molecules (X = S H , CI, Br) With Dinuclear Palladium(I) Complexes Containing Bis(diphenylphosphino)methane by Freddy A . Barnabas  B. Sc. (Chemistry) Madras University, India, 1975 M.  A  Sc. (Chemistry) Madras University, India, 1977  THESIS T H E  SUBMITTED  IN  REQUIREMENTS M A S T E R  PARTIAL  FULFILMENT  F O R T H E DEGREE O F  OF  SCIENCE  in T H E  FACULTY O F G R A D U A T E  STUDIES  CHEMISTRY  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA March 1989 © Freddy A. Barnabas, 1989  O F  In  presenting  degree freely  at  this  the  available  copying  of  department publication  of  in  partial  fulfilment  University  of  British  Columbia,  for  this or  thesis  reference  thesis by  this  for  his thesis  and  study.  scholarly  or for  her  of  financial  CJ\Cm l$>b^j  The University of British Columbia Vancouver, Canada  DE-6  (2/88)  I  I further  purposes  gain  the  shall  requirements  agree  that  agree  may  representatives.  permission.  Department  of  be  It not  that  the  Library  by  understood be  an  allowed  advanced  shall  permission for  granted  is  for  the that  without  make  it  extensive  head  of  copying my  my or  written  Abstract  This thesis describes kinetic and spectroscopic studies on the reaction between Pd X (dpm) , 1 (X = CI, a; Br, b; I, c; dpm = bis(diphenylphosph2  2  2  ino)methane) and HX molecules (X = SH, CI, Br) in solution. The reaction of 1 with hydrogen sulfide leads to the formation of the corresponding /i-sulfide, 2, and H gas. Kinetic studies carried out in CH2CI2 solutions over the temper2  ature range 0 - 35°C reveal a first order dependence on both palladium dimer and hydrogen sulfide concentrations. The value of the bimolecular rate constant, k , is 1.71 x I O M -3  _ 1  2  s  -1  at 25°C, and the activation parameters for the  reaction are AH* = 55 ± 5 kJ mole" and AS* = -115 ± 10 J K" mole" . 1  1  1  Low temperature H and P{ H} nmr spectroscopic investigations compleJ  31  1  ment the kinetic studies, and show that the reaction proceeds via the formation of a hydride intermediate.  The observations indicate that the reaction  proceeds through oxidative-addition of H S across the metal-metal bond and 2  the data are discussed in terms of the following reactions: Pd X (dpm) + H S 2  2  2  2  v  _  Pd X (dpm) (H S)  =^  Pd X (dpm) (H)(SH)  2  2  2  2  1 Pd X (dpm) (H S) 2  2  2  2  v  Pd X (dpm) (H)(SH) 2  2  •  2  2  2  2  Pd X (dpm) ( -S) + H 2  2  2  M  2  2 There is no direct evidence for the first reaction listed, however. The analogous reactions between 1 and HX (X = CI, Br) were studied with UV-visible, *H and P{ H} nmr spectroscopy. 31  1  ii  The reaction between  HCl and l a in CH C1 results in the 'direct' formation of Pd(II) monomer, 2  2  PdCl (dpm), with no intermediates being seen. The corresponding reaction 2  between the bromide, l b and HBr, however, is seen to take place in several steps. Reaction with one mole of HBr results in the formation of a hydride intermediate; this then reacts with a second mole of HBr to form H gas and 2  a tetrabromo complex, Pd Br (dpm) , which subsequently fragments slowly 2  4  2  to the Pd(II) monomer, PdBr (dpm). All the intermediate species involved in 2  the bromide/HBr reaction were detected by UV-visible and low temperature J  H and P{ H} nmr spectroscopy. 31  J  An effective way of abstracting the bound //-sulfide ligand in order to regenerate the palladium dimer, 1, has been demonstrated using reactions with dpm and with diphenyl; the abstraction by dpm results in formation of dpmS, the monosulfide of dpm, as the only sulfur-containing product. A new and as yet incompletely characterized system that catalytically desulfurizes H S was generated by having excess dpm present in the reaction between lb 2  and H S. This catalytic system tranfers sulfur from H S to the bisphosphine 2  2  dpm to form dpmS along with some uncharacterized palladium compounds.  in  Table of Contents  Abstract  Table of Contents  List of Figures List of Tables List of Abbreviations Acknowledgement 1  2  INTRODUCTION 1.1  General introduction  1.2  Transition metal/H S chemistry  1.3  The chemistry of transition metal dpm dinuclear species  1.4  Aim of work  1.5  References  2  EXPERIMENTAL 2.1  MATERIALS 2.1.1  Solvents  2.1.2  Gases  2.1.3  Phosphines and other materials  2.1.4  Palladium Compounds 2.1.4.1  Pd(PhCN) Cl  2.1.4.2  Pd,(dba) .CHCl  2  s  iv  2  s  . . .  Pd Cl (dpm)  2.1.4.4  Pd Br (dpm)  2.1.4.5  Pd I (dpm) .CH Cl  2.1.4.6  Pd Cl (dpm) t>S)  22  2.1.4.7  Pd Br (dpm) (/i-S)  23  2.1.4.8  Pd I (dpm) (/x-S)  23  2.1.4.9  PdCl (dpm)  24  2.1.4.10  PdBr (dpm)  24  2  2  2  2  2  2  2  2  21  2  2  2  2  21  2  2  2  2  20  2  2  2  2  2  2  2.2  Instrumentation  25  2.3  Procedure for a typical kinetic run  26  2.4  Low temperature nmr experiments with P d X ( d p m ) and H S .  28  2.4.1  Reaction of P d B r ( d p m ) with H S 2  28  2.4.2  Reaction of Pd I (dpm) with H S  -28  2.5  2.6  3  2.1.4.3  2  2  2  2  2  2  2  2  2  2  2  Interaction of P d B r ( d p m ) with H X  29  2.5.1  Room temperature reaction  29  2.5.2  Low temperature reaction  29  2  2  2  Sulfur abstraction reactions  29  2.6.1  Sulfur abstraction by dpm  29  2.6.2  Desulfurization o f H S  30  2  2.7  Gas solubility measurements  30  2.8  References  31  T H E I N T E R A C T I O N O F H S W I T H Pd(I) D I M E R S 2  d p m dimer, P d X ( d p m )  32  3.1  T h e paHadium(I)  3.2  Reaction with D S  33  3.3  Kinetics and rate measurements  34  2  2  v  2  2  32  3.4  4  Spectroscopic detection of intermediates  45  3.4.1  Reaction between Pd Br2(dpm) and H S 2  45  3.4.2  Reaction between Pd I (dpm) and H S  49  2  2  2  2  2  2  3.5  Discussion of kinetic and spectroscopic data  52  3.6  References . .  61  THE INTERACTION  OF HX  (X  =  CI, B r ) W I T H  Pd(I)  DIMERS  64  4.1  Introduction  64  4.2  Stoichiometry of the reaction and product identification . . . .  67  4.2.1  Reaction of P d C l ( d p m ) with H C l at room temperature 67  4.2.2  Reaction of Pd Br (dpm) with HBr at room temperature 70  4.2.3  Low temperature spectroscopic studies of the reaction  2  2  2  2  2  2  between l b and HBr  5  6  75  4.3  Discussion  78  4.4  References  83  SULFUR TRANSFER REACTIONS  84  5.1  Introduction  84  5.2  Sulfur abstraction reactions  87  5.2.1  Sulfur abstraction by phosphines  87  5.2.2  Sulfur abstraction by organics  88  5.3  The desulfurization of H S  90  5.4  References  94  2  GENERAL CONCLUSIONS 6.1  96  Conclusions  96  vi  Recommendations for future work  vii  List of Figures  2.1  Anaerobic spectral cell used for UV-visible spectroscopy  27  3.1  Visible absorption spectral changes of a CH2CI2 solution of Pd Br2(dpm)2 upon addition of H S at 25°C  3.2  35  2  2  Rate plot for the reaction between Pd Br (dpm)2 (1.01 x 10 2  -3  2  M) and H S (0.53 M) in CH C1 , at 25°C 2  3.3  2  36  2  A rate plot analysed for first order Pd\ dependence in CH C1 2  2  at 25°C. ([Pd ] = 1.01 x 10" M and [H S] = 0.53 M)  37  3.4  Solubility of H S in CH C1 at various pressures  40  3.5  Dependence of reaction rate on [Pd\] in CH C1 at 25°C  42  3.6  Dependence of reaction rate on [H S] at 1.01 x 10~ M Pd in  !  3  2  2  2  2  2  2  2  3  2  2  CH C1 at 25°C 2  3.7  43  2  Temperature dependence of the rate constant for the reaction between l b (at 1.01 x 10" M) and H S in CH C1  44  3  2  3.8  2  2  The H nmr spectra in CD C1 solution for (A) - C H - region of J  2  2  2  l b ; (B) - C H - region of l b + H S at -70°C and (C) hydride 2  2  region of l b + H S at -70°C  46  2  3.9  The H nmr spectra in CD C1 solution of (A) - C H - region 1  2  2  2  of l b + E S warmed up to room temperature and (B) - C H 2  2  region of 2b 3.10  The  3  1  P {  1  47  H } nmr spectra in CD C1 of l b and H S 2  viii  2  2  48  3.11  T h e H n m r spectra in C D C 1  s o l u t i o n for ( A ) - C H - region of  !  2  2  2  l c ; ( B ) - C H - region of l c + H S kept at ~ - 7 4 ° C for 8 h a n d 2  2  ( C ) - C H - region of l c + H S k e p t at ~ - 7 4 ° C for 8 h t h e n w a r 2  2  m e d u p to - 4 0 ° C 3.12  The E 1  50  n m r spectra in C D C 1 2  s o l u t i o n of ( A ) l c + H S kept  2  2  at — 7 4 ° C for 8 h ( h y d r i d e a n d - S H region) a n d ( B ) 2 c 3.13  The  3 1  P { H } n m r spectra in C D C 1  51  of ( A ) l c at 2 0 ° C ; ( B )  1  3  lc  + H S kept at — 7 4 ° C for 8 h a n d ( C ) l c + H S kept at 2  2  — 7 4 ° C for 8 h a n d then w a r m e d u p to - 4 0 ° C 3.14  T h e ^ P ^ H } n m r spectra in C D C 1  3  53  of ( A ) l c + H S kept at 2  ~ - 7 4 ° C for 8 h a n d t h e n w a r m e d to r o o m t e m p e r a t u r e a n d ( B ) a u t h e n t i c s a m p l e of 2 c at 2 0 ° C 4.1  The  3 1  54  P { H } n m r s p e c t r a of t h e r e a c t i o n p r o d u c t s of l b J  and  anhydrous H C I  65  4.2  T h e mechanistic pathway of the reaction between l b a n d B r .  4.3  T h e H n m r spectra ( - C H - region) i n C D C 1  2  :  2  3  s o l u t i o n at 2 0 ° C  of ( A ) l a ; ( B ) l a + H C l ( g ) ( ~ 3 : 1 ) a n d ( C ) l a + H C l ( g ) (1:2). 4.4  The  3 1  P { H } n m r spectra in C D C 1 1  3  68  s o l u t i o n at 2 0 ° C of ( A ) l a ;  ( B ) i a + H C l ( g ) ( ~ 3 : 1 ) a n d ( C ) l a + H C l ( g ) (1:2) 4.5  66  69  T h e gas c h r o m a t o g r a m s o f (A) t h e gaseous p r o d u c t s e v o l v e d i n t h e r e a c t i o n o f l a + 2 H C l ( g ) i n DMA;  ( B ) t h e gaseous p r o d u c t s  e v o l v e d i n t h e r e a c t i o n of l b + 2 H B r ( g ) i n C H C 1 2  a u t h e n t i c d i h y d r o g e n gas  2  and (C) 71  ix  4.6  Visible absorption spectrum of l b upon addition of anhydrous HBr at 25°C, as a function of time  4.7  72  The *H nmr spectra (-CH - region) in CDC1 solution at 20°C 2  3  of (A) l b ; (B) l_b 4 HBr(g) after 15 min; (C) l b 4 HBr(g) after 6 h and (D) authentic sample of PdBr (dpm) 2  4.8  73  The P { H } nmr spectra in CDC1 solution at 20°C of (A) 31  1  3  l b ; (B) l b 4 HBr(g) after 15 min; (C) l b + HBr(g) after 6 h and (D) authentic sample of PdBr (dpm)  74  2  4.9  The H nmr spectra (-CH - region) in CDC1 solution at -40°C ]  2  3  of (A) l b 4 HBr(g) (2:1); (B) l b 4 HBr(g) (1:2) after ~15 min and (C) l b 4 HBr(g) (1:2) after - 3 0 min 4.10  76  The H nmr spectra in CDC1 solution at -40°C of (A) l b 4 J  3  HBr(g)(l:l), the high field region after ~ 2 min; (B) l b 4 HBr(g) (1:2) after 60 min, - C H - region and (C) l b 4 HBr(g) 2  (1:2) after 6 h , - C H - r e g i o n  77  2  4.11  The ^P-^H} nmr spectra in CDC1 solution at -40°C of (A) 3  l b 4 HBr(g) (1:2) after ~15 min; (B) l b -f HBr(g) (1:5) after ~20 min and (C) l b 4 HBr(g) (1:10) after ~25 min 5.1  The schematic representation of the regeneration of 1 from 2 by the oxidation of the /i-sulfide to S 0  5.2  2  86  The mechanistic, pathway for the abstraction of sulfur by dpm from 2  5.3  79  89  The P { H } nmr spectra of the reaction product of lc and 31  1  H S in the presence of 20-fold excess dpm 2  x  91  5.4  The HS 2  3 1  P { H } nmr spectra of the reaction product of lh X  i n the presence of 20-fold excess dpm  xi  and 92  List of Tables  III-2 Solubility of H S in C H C l 2 at various pressures at 25°C. . . .  39  III-2 Dependence of reaction rate on [Pd\] in C H C 1 at 25°C.  39  2  2  2  2  . . .  III-3 Dependence of reaction rate on [H Sj at 1.01 x 10" M P d in 3  2  CH C1 2  2  2  at 25°C  41  III-4 Temperature dependence of the rate constant for the reaction between l b and H S in C H C 1 2  2  2  xii  41  List of Abbreviations  The following list of abbreviations, most of which are commonly adopted in chemical literature, will be employed in this thesis.  br  broad  Cp  cyclopentadienyl,  d  doublet  dba  dibenzylideneacetone,  dd  doublet of doublets  DMA  N,N'-dimethylacetamide, CH CON(CH )  dpm  bis(diphenylphosphino)methane, ( C H ) P C H P ( C H 5 )  dpmS  bis(diphenylphosphino)methane monosulfide,  C5H5  C H CH:CHC(0)CH:CHC H 6  5  6  3  3  6  5  5  2  2  2  6  2  (thio(diphenyl)phosphino(diphenyl)phosphinomethane), (C H ) PCH P(S)(C H ) 6  dpmS  2  5  2  2  6  5  2  bis(diphenylphosphino)methane disulfide, (bis(thio(diphenyl)phosphino)methane), (C H ) P(S)CH P(S)(C H ) 6  5  2  2  6  5  2  dpe  l,2-bis(diphenylphosphino)ethane, ( C H ) P C H C H P ( C H 5 )  i.r.  infra-red  J  couphng constant, Hz  m  multiplet  31  6  P{ H} 1  PPh  3  triphenylphosphine, (C H ) P 6  5  3  triphenylphosphine sulfide, (C H ) P(S)  PPh Me  methyldiphenylphosphine, (C H ) PMe  Pd*  Pd X (dpm)  2  2  proton broad-band decoupled phosphorus nmr  PPh S 3  6  6  6  2  2  5  5  3  2  2  xiii  2  2  6  2  q  quintet  s  singlet or second  t  triplet  UV  ultra-violet  X  halide ligand, CI, B r , or I  8  chemical shift, p p m  e  molar extinction coefficient or dielectric constant  Some of the compounds used during the course of this work have been referred to by numerical symbols in this thesis for the sake of brevity and simplicity. Following is the list of complexes corresponding to each such symbol:  1  Pd X (dpm)  la  Pd Cl (dpm)  lb  Pd Br (dpm)  lc  Pd I (dpm)  2  Pd X (/i-S)(dpm)  2a  Pd Cl (/x-S)(dpm)  2b  Pd Br (/*-S)(dpm)  2c  Pd I (/i-S)(dpm)  3b  Pd Br (d m) (H)(SH)  3c  Pd I (dpm) (H)(SH)  4b  Pd Br (dpm) (H)(Br)  5b  Pd Br4(dpm)  6a  PdCl (dpm)  6b  PdBr (dpm)  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  P  2  Pd Br (dpm) 2  2  s  2  2  2  2  2  2  2  2  2  2  2  Pd Br (M-S)(dpm)  2  2  xiv  2  5  Acknowledgements  I am  most grateful to Professor B. R. James for his guidance and encour-  agement throughout the course of this work. I would also like to express my  gratitude to the members of Professor  James'group for making valuable suggestions regarding this work. I am also indebted to Dr. Dominique Sallin and Mr. Ken MacFarlane for their support, friendship and suggestions. Special thanks must go to Dr. K. Venkateswaran, who  helped me w i t h plots and text processing. The assistance and cooperation of various departmental services are grate-  fully acknowledged.  xv  Chapter 1  INTRODUCTION  1.1  General introduction  Recent studies carried out i n this laboratory to separate CO from gas mix1  tures using Pd(I) dimers of the type P d X ( d p m ) 2  2  2  ( X = CI, B r , I; d p m =  P h P C H P P h ) led to the discovery of reaction 1.1, while testing the reactiv2  2  2  ity of the palladium complex toward H S , an impurity often present i n such 2  gas mixtures. Pd X {dpm) 2  2  + HS  2  2  —• Pd X (dpm) (fi 2  2  2  - S) + H  (1.1)  2  [X = Cl,Br,I] For X = CI and B r the reaction is quantitative and is the first of its kind i n which hydrogen gas is generated from H S by a transition metal complex i n 2  solution. Gaseous H S , a noxious pollutant, is produced as a result of both natural 2  and man-made processes. T w o main mechanisms account for the generation of 2  the gas i n the natural sources: bacterial reduction of sulfate, sulfur and organic sulfur compounds i n plant a n d animal matter, and geochemical formation as in volcanic activity and thermal hot springs. These natural sources contribute an important part of atmospheric emission of H S (3 - 30 /ig/m ) that is part 3  2  of the natural global sulfur cycle.  1  Though significant quantities of H2S are generated in many industrial processes, most of it is consumed for the production of S and SO2.  Important  production sources include petroleum refining operations, natural gas plants, petrochemical plants, coke oven plants and kraft pulp mills; H2S is an occasional pollutant, and the main pollution sources are gas-well blow outs and pulp mills.  2  Though H2S is as toxic as cyanide to most organisms, nature has evolved a few microbes, that depend on it for their survival. For example, a class of 3  bacteria known as 'sulfate reducers' produce H S 2  in anoxic conditions. The generated H S 2  by the reduction of sulfates  is utilized in turn by other types of  bacteria, and the subsequent oxidation results i n elemental sulfur and sulfate. It is interesting to note that most of the world's native sulfur deposits are said to be formed as a result of bacterial action during the warm and sunny Permian and Jurasic periods (~ 2 x 10  8  years ago).  As a result of a geochemical reaction that takes place at a newly formed ocean floor, H2S is generated. W h e n sulfate bearing sea water percolates and 4  comes i n contact with hot crustal rocks, iron present i n the rock reduces the sulfate to H2S  gas.  Thus the hot water, rising to the ocean floor through  the so-called 'hydrothermal  vents' or 'hot springs', is heavily charged w ith r  hydrogen sulfide. In the waters surrounding these vents, nature has evolved a ecosystem that solely depends on a bacterium that derives energy by oxidizing H2S to sulfate. This unique, diversified, ecosystem apart from the bacterium includes giant worms, clams and crabs that tolerate the high concentration of H2S and perhaps are the only higher organisms unaffected by H S . 2  The fossil fuels, petroleum, shale, oil bearing sands, coal and natural gas have varying amounts of sulfur depending on their origin.  For example, i n  petroleum the sulfur is mainly present as mercaptans (RSH), sulfides (RSR), disulfides (RSSR) and sulfur heterocyclics. The presence of sulfur organics in 5  fossil fuels has the following implications: (i) the refining of petroleum involves the catalytic cracking and catalytic reforming processes that utilize transition metal catalysts. If sulfur organics are not removed prior to these processes, then the catalysts are rendered ineffective by poisoning. (ii) Combustion of sulfurous fossil fuels produces sulfur oxides (mainly S 0 ) 2  that are not only corrosive to the machinery but if vented into the atmosphere cause many environmental problems. It is interesting to note that a substantially larger amount of SCs than it is utilized industrially is discharged into the atmosphere. Acid rain, smog and other environmental 6  hazards result because of this discharge. Thus sulfur removal is essential and is removed from petroleum by a process called hydrodesulfurization(HDS), prior to the cracking and reforming. In HDS processes, organic sulfur is removed as H S by reacting with H gas in 2  2  the presence of sulfided M o - C o or W - N i oxide catalysts as in reactions 1.2 to 1.5.  5  RSH + H —>RH 2  RSR + 2H —>2RH 2  RSSR + 3H —>2RH 2  C H S(thiophene) 4  4  2  + HS  (1.3)  + 2H S  (1.4)  2  + 2H —• CH = CH-CH 2  2  (1.2)  + HS  2  = CH + H S 2  2  (1.5)  The resulting H S is either oxidized to elemental sulfur (as in Claus, Stretford, 2  Takahax, Giammarco-Vetrocoke-sulfur and Konox processes ) or converted to 7  3  C a S 0 . In the currently available technologies, the industrially expensive H 4  2  is lost and thus sulfur removal becomes an expensive process especially for petroleum crude w i t h high sulfur content.However, the organic sulfur removal could become an industrially less expensive operation w i t h little or no consumption of H , provided H 2  2  could be generated from H S by  a catalytic  2  process, perhaps one based on reacion 1.1.  Such a process would be valuable,  if not now, at least i n the future, once currently usable petroleum reserves of low sulfur content become exhausted. Thus the study of the interaction of H S with transition metal complexes, 2  as i n reaction 1.1,  is of fundamental importance because of the biological,  environmental and industrial importance of the gas. Further, the interesting reactivity pattern of H S, as exhibited in reaction 1.1, could lead to the devel2  opment of an efficient catalytic system, perhaps a homogeneous one (the first of its kind) to desulfurize H S. 2  1.2  Transition metal/H S chemistry 2  Transition metals and sulfur have an 'affinity' for one another and readily form metal sulfides. This strong tendency to form metal sulfides can be readily seen in the Pearson's acid-base scale, where d"- transition metal ions (with higher 8  n values) and sulfide ions are both classified as 'soft' groups. The interaction of H S w i t h transition metal complexes typically gives insoluble sulfides often 2  polymeric i n nature, but more interesting reactivity patterns are known. The first reported case of quantitative H  2  generation from H S by a transition metal 2  complex was unearthed i n this laboratory as noted in sec 1.1.  This involved  la  the insertion of S between the P d - P d metal-metal bond of P d X ( d p m ) , X 2  4  2  2  = CI, B r and I, to give a //-sulfide complex of the type Pd2X2(dpm) (/x-S), 2  Pd X {dpm) 2  2  + H S — • Pd X {dpm) {fi  2  2  2  [X =  2  -S)  2  + H  (1.6)  2  Cl,Br,I]  Apart from this reaction, there is only one other system that generates H2 quantitatively from H S.  9  2  2C ' Zr{CO) P 2  + 2H S—>  2  [Cp' Zr(fi  2  [Cp = T J - C H 1  - S)] + 2H + ACO  2  5  &  5  5  The interaction of H S with the ruthenium complexes 2  and Ru(CO)2(PPh3)3,  results i n H production. T h e H  12  (1.7)  2  or r, - C M e ]  5  5  2  2  2  RuH (PPh )4,  1 0 , 1 1  3  2  generated from the  reaction of RuH (PPh3)4 and H2S is a consequence of the hydride content of 2  the complex, and the net reaction, ignoring a labelling of the hydrogen atom, is the more usual oxidative addition of H2S v i a cleavage of the S-H b o n d . RuH {PPh ) 2  3  + H S —» RuH(SH){PPh )  4  2  3  The ruthenium complexes, R u ( C O ) ( P P h ) 2  3  1 2 3  + H + PPh  3  2  (1.8)  3  and [ R u ( N H ) ( H S ) ] , 2 +  3  1 1 - 1 3  5  1 4  2  reduce H2S to H2 and 2 S H " . Ru(CO) {PPh ) 2  3  + HS  3  RuH{SH)(CO)(PPh )  2  3  Ru(SH) (CO) {PPh ) 2  2\Ru{NH \{H S)) + 2  3  2  2  3  -f H  2  -^2[Ru(SH){NH ) f  +  3  B  2  (1.9)  2  + H  2  (1.10)  The reaction was suggested tentatively because the precursor complex was not. obtained i n a pure state. T h e only other well characterised isolated H2S com14  plex appears to be W ( C O ) ( H S ) , 6  2  1 6  although H n m r spectroscopic evidence X  5  has been presented for the species Pt(PPh3)2(H2S) en route to formation of more stable (hydrido)(mercapto) c o m p l e x .  Equation 6, analogous to Eqs 1  16,17  and 2, has been invoked for a solid state reaction to account for the filling of vacant anionic sites by sulfur i n W S  2W  + HS  3+  1.3  A  2  n  i  ^  lattices.  2  t  i  t  e  18  2W  4+  + S- + H  (1.11)  2  2  T h e c h e m i s t r y of t r a n s i t i o n m e t a l d p m d i n u c l e a r s p e c i e s  The bisphosphine, bis(diphenylphosphino)methane  (dpm), has proved to be  a versatile ligand for linking two metals while allowing for considerable flexibility in the distance between the two metal ions involved. Though dinuclear metal complexes of dpm are known w ith one, T  two  19  or t h r e e  2 0  21  bridging fx-  dpm ligands, two trans-/z-dpm ligands are most common and these include homobimetallic R h , Pd/Fe  2 8  lr,  22  and P d / M n  2 9  2 3  Pd,  2 4  Pt  2 5  and M n  2 6  a n d heterobimetallic  Pd/Pt,  27  dinuclear complexes. Typically, these dinuclear com-  plexes exhibit any one of three main structural types. Firstly, a structure without either a metal-metal  bond or other bridg-  ing groups between the two metal centers and the two metal ions are linked by two bridging d p m ligands. This structure is most common w i t h dimers a n d is more elusive w i t h other metals; R h ( C O ) C l ( d p m ) 2  Rh (MeNC)4(dpm) 2  3 1 2  2  2  3 2  Rh(I) 0  and  are good examples of complexes having this structure,  usually described as a face-to-face structure. T h o u g h face-to-face dinuclear complexes are known i n the Pt(II) and Pd(II) systems, P t ( C = C R ) ( d p m ) 2 2  ( R = Me, C F , P h , 4 - t o l y l ) 3  32  and P d C l ( C H ) ( d p m ) , 2  2  3  2  2  3  3  4  those w i t h other  non-bridging, terminal ligands (i.e. X i n M X 4 ( d p m ) ) rearrange rapidly to 2  monomelic forms.  34  6  2  Secondly, a structure with no other bridging groups but with interaction between the metal centres is commonly adopted by both homo- and heterobimetallic complexes of dpm.The bond between the two metal centres is usually single for the majority of metals, but i n certain M o and Re s y s t e m s  multiple  35  bonds are known. T h e singly metal-metal bonded derivatives, MM'X2(dpm)2 ( M , M' = P d , P t ; X = CI) display high reactivity either by displacement of terminal chloride ligands by anionic or neutral ligands or by insertion of SnCl  2  into the metal-chloride b o n d .  240  '  250,36  T h e displacement of the terminal  chloride is effected by various ligands including B r ~ , I , N C O , N C S ~ , N j , -  -  N O 3 , this resulting i n the alteration of the metal-metal bond strength. T h e change of bond strength is attributed to the trans-influence exerted by the terminal ligand. A s a result, the reactivity of the metal-metal bond is altered and this is evident i n most of the reactions i n which the metal-metal bond is broken.  However, i n the reaction between C O and P d X 2 ( d p m ) 2  2  species  ( X = CI, B r , I, N C O ) , the rate was governed b y the P d - C O bond strength rather than P d - P d bond energy.  37  A number of unique chemical features have  been observed as a result of the proximity of the two metal ions i n the d p m complexes. M a n y of these complexes are able to co-ordinate (sometimes reversibly), i n a bridging manner, atoms or small molecules such as H, S  la,25a,39 g 4 0 g Q ^ B a . S M l  C  S 22a,25a  e  2 )  and CH2.  C  N  R  24.25«,36,45  20,24fc,25o,33,  SQ42  C  0  36,46  20,24,25a,37,43 RQ~,  Q^R-,  47  N  j  R  +  )  4  4  RS",  20,24b,36  2  6  0  20,24,250  CN",  2 6  '  38  °  N C R R ' *>>*">** 2  ' This type of co-ordination results i n the t h i r d structural w  type that includes both A-frame structures w i t h one bridging group, and double A-frame structures with two bridging groups. B o t h single and double atom bridges are known; C H , C O , S 0 and P h N j connect the metals centres v i a 2  2  single atoms while CS2 and R C = C R utilise two atoms. A metal-metal bond 7  may  be present in complexes with either one and two bridging groups. In dinuclear P d complexes of the type P d X 2 ( d p m ) , a structure with a 2  2  single metal-metal bond exists. However, in the analogous A-frame complexes with a single bridging group, the P d - P d bond is absent. The terminal, nonbridging l i g a n d s  (i.e. X and X' in P d X X ' ( d p m ) ) can be simple inorganic  24a  2  2  anions such as C I " , B r " , I , NCS~,  N ,  organic groups hke CeFs,  or C6H S. ° Complexes are also known  -  36  CeCls,  36  NCO  3  or predominately  -  non-ionic  24  5  with two different terminal ligands. In these mixed terminal ligand dimers,  C C1 6  5  or CeFs is usually one of the ligands and the other terminal ligand is  usually a simple inorganic anion mentioned above. Both types of P d  dimers with the same or mixed terminal ligands exhibit  2  reactivity toward the insertion of small molecules. The reactivity is, however, altered considerably by changing the terminal ligands. For example, the insertion shows such a reactivity trend by changing ligands (CI, Br, I, but the resulting p-CO  complexes are isolable.  or both terminal ligands, C O  37  inserts but the fi-CO  complex is n o n - i s o l a b l e The insertion of S0 ,  5  or C e C l ; spontaneous loss of S0 5  CI, B r or I . 2  complexes  occurs above 0°C  2  3  2  (dmpm)  49  and P h P C H ( C H ) P P h 2  3  2  with  when X  (dpmMe)  ally exhibit reactivity toward the insertion of small molecules. P d X ( d p m M e ) ( d p m ) species ( X = CI, Br, I, NCO), 2  36  =  Dinuclear complexes with related bisphosphine ligands such as  4 1 a  (CH ) PCH P(CH ) 3  2  2  36  on  2  the other hand, results i n the formation of stable / / - S 0 = CeF  NCO),  W i t h CeFs or CeCls as one  and is observed only as a transient intermediate.  X  CO  2  CO  sertion from H S, take place, but w i t h P d X ( d p m M e ) 2  neither the insertion of C O  2  2  2  42  gener-  In the case of  insertion, and S i n ( X = CI, Br, I,  NCO)  or S occurs because of steric factors imposed by  the additional methyl group. 8  1.4  Aim  of w o r k  The main objective of this thesis was to investigate in greater detail the kinetic and mechanistic aspects of reaction 1.1, the first of its kind to show full recovery of H2 from H2S. This study was aimed at answering some of the pertinent questions connected with reaction 1.1, such as the possible role of the acidic -CH2- protons of dpm, the nature of attacking species, the nature of reaction intermediates, the reasons for the non-reactivity of other sulfur compounds (RSH  and R S S R )  4 6  and the effect of solvent polarity (i.e. dielectric constant).  Further aims of the project were to study the reactivity of the P d X ( d p m ) 2 2  2  dimers with analogous H X molecules ( H C l , H B r and HI), and to find an effective way to remove the sulfur from the fi-S complex in order to regenerate the P d dimer.  9  1.5  References  1. (a) C . L . Lee, G . Besenyei, B . R . James, D . A . Nelson and M . A . Lilga, J. Chem. Soc,  Chem.  Commun.,  1175 (1985).  (b) S. E . Lyke, M . A . L i l g a , D . A . Nelson, B . R . James and C . L . Lee, Ind. Eng. Chem. Prod. Res. Dev., 25, 517 (1986). 2. (a) Hydrogen sulphide - Environmental  technical information for problem  spills, Environmental Protection Service, Ottawa, O N , C a n a d a , (1984), p.26. (b) Hydrogen sulfide in atmospheric environment: assessing its effects on environmental  Scientific criteria for  quality, N R C C No.  18467, Na-  tional Research Council of C a n a d a , Ottawa, O N , Canada, (1981). 3. (a) J . R. Postgate, The sulphate-reducing  bacteria, 2  nd  edition, C a m -  bridge University Press, Cambridge, (1984), p.61. (b) J . R. Postgate, New Scientist (July 1988), p.58. 4. (a) J . E d m o n d , Scientific American,  (April 1983), p.78.  (b) J . E d m o n d , Oceanus, (Summer 1982), p.22. 5. S. C . Schuman and H . Shalit, Cat. Rev., 4, 245 (1970). 6. TJ. H . F . Sander, H . Fischer, U . Rothe and R . K o l a , Sulphur, sulphur dioxide and sulphuric acid, Verlag Chemie International Inc., Deerfield Beach, F l . , U S A , (1984), p.241. 7. U . H . F . Sander, H . Fischer, U . Rothe and R . K o l a , Sulphur, sulphur dioxide and sulphuric acid, Verlag Chemie International Inc., Deerfield Beach, F l . , U S A , (1984), p.41. 10  8. R. G. Pearson, J. Am.  Chem. Soc, 85, 3533 (1963).  9. F. Bottomley, D. F. Drummond, G . 0. Egharevba a n d P. S . White, organometallics,  5, 1620 (1986).  10. K . Osakada, T. Yamamoto, A. Yamamoto, A. Takenaka and Y. Sasada, Inorg. Chim. Acta, 105, L 9 (1985). 11. K . Osakada, T. Yamamoto, A. Yamamoto, Inorg.  Chim.  Acta, 90, L 5  (1984). 12. C. L. Lee, J . Chisholm, B. R. James, D. A. Nelson and M. A. Lilga, Inorg. Chim. Acta, 121, L 7 (1986). 13. A. M. Mueting, P. Boyle and L. H. Pignolet, Inorg.  Chem., 23, 44  (1984). 14. G . C. K u e h n a n d H. T a u b e , J. Am. 15. M. Herberhold a n d G . Suss, Angew.  Chem. Soc, 98, 689 (1976). Chem.  Int.  Ed. Engl,  15, 366  (1976).; J. Chem. Res., 57, 246 (1977). 16. D. Morelli, A. Segre, R. Ugo, G . L a Monica, S. Cenini, F. Conti and F. Bonati, J. Chem. Soc,  Chem. Commun.,  524 (1967).  17. R. U g o , G . L a M o n i c a , S . C e n i n i , a n d F. C o n t i J. Chem. Soc  (A), 522  (1971). 18. B . C . G a t e s , J . R. K a t z e r a n d G . C . A. S c h u i t , Chemistry Processes, M c G r a w - H i l l , N e w Y o r k , 1979, C h . 5.  11  of  Catalytic  19. See, for example, (a) P. A. Wegner, L. E. Evans and J . Haddock, Inorg. Chem., 14, 192 (1975). (b) F. A. Cotton and J. M. Troup, J. Am.  Chem. Soc, 96, 4422 (1974).  (c) B. P. Sullivan and T. J . Meyer, Inorg. Chem., 19, 752 (1980). 20. See, for example, R. J . Puddephatt, Chem. Soc. Rev., 12, 99 (1983). 21. (a) E. W . Stern and P. K . Maples, J. Catol., 27, 120 (1972). (b) K . A. Azam, R. J. Puddephatt, M. P. Brown and A. Yavari, J. Chem., 234, C31 (1982).  Organomet.  22. See, for example: (a) M. Cowie and S. K . Dwight, J. Organomet.  Chem., 214, 233 (1981).  (b) C. Woodcock and R. Eisenberg, Organometallics,  1, 886 (1982).  (c) J . T. Mague, Inorg. Chem., 22, 45 (1983). (d) C. Woodcock and R. Eisenberg, Organometallics,  4, 4 (1985).  (e) J . A. Ladd, M. M. Olmstead and A. L. Balch, Inorg.  Chem., 2 3 ,  2318 (1984). 23. (a) B. R. Sutherland and M. Cowie, Organometallics,  3, 1869 (1984).  (b) J . T. Mague, C. L. K l e i n , R. J . Majeste and E. D. Stevens, Organometallics,  3, 1860 (1984).  24. (a) A. L. Balch, i n Catalytic Aspects of Metal Pkosphine  Complexes,  E d i t e d by E. C. Alyea and D. W. Meek, Advances i n Chemistry Series 196, Am.  Chem. Soc, Washington, D.C. (1982) p.243.  12  I  (b) A. L. Balch, i n Homogeneous  Catalysis with metal Phosphine  Com-  plexes, Edited by L. Pignolet, Plenum, New York (1983) p.167. 25. See, for example, (a) M. P. Brown, J . R. Fisher, S. J . Franklin, R. J . Puddephatt and M. A. Thomson, i n Catalytic Aspects of Metal Phosphine  Complexes, Edited  by E. C. Alyea and D. W. Meek, Advances i n Chemistry Series 196, Am. Chem. Soc, Washington, D. C. (1982) p.231. (b) A. T. Hutton, B. Shebanzadeh and B. L. Shaw, J. Chem. Chem. Commun.,  Soc,  549 (1984).  (c) P. G. Pringle and B. L. Shaw, J. Chem.  Soc,  Dalton Trans., 849  (1984). (d) M. C. Grossel, J . R. Batson, R. P. M o u l d i n g and K. R. Seddon, J. Organomet.  Chem., 304, 391 (1986).  26. See, for example, (a) H. C. Aspinall, A. J . Deeming and S. Donovan-Mtunzi, J. Chem. Soc,  Dalton Trans., 2669 (1983).  (b) G. Ferguson, W. J . Laws, M. Parvez and R. J . Puddephatt, Organometallics,  2, 276 (1983).  (c) H . C. A s p i n a l l and A. J . Deeming, J. Chem.  Soc,  Dalton  Trans.,  743 (1985). 27. P. G. Pringle a n d B. L. Shaw, J. Chem.  Soc,  Chem.  Commun.,  81  (1982). 28. G. B. Jacobson and B. L. Shaw, J. Chem. (1987).  13  Soc,  Dalton Trans., 2005  29. (a) P. Braunstein, J . M. J u d and J. Fischer, J. Chem. Commun.,  Soc,  Chem.  5 (1983).  (b) B. F. Hoskins, R. J. Stein and T. W. Turney, Inorg.  Chim.  Acta,  77, L69 (1983). (c) P. Braunstein, C. de Meric de Bellefon and M. Ries,  Organometallics,  7, 332 (1988). 30. A. L. Balch, J. W. Labade and G. Delker, Inorg. 31. (a) A. L. Balch, J. Am.  Chem.  Soc,  Chem.,  18, 1224 (1979).  98, 8049 (1976).  (b) J. T. Mague and S. H. DeVries, Inorg.  Chem.,  19, 3743 (1980).  32. R. J. Puddephatt and M. A. Thomson, J. Organomet.  2 3 8 , 231  Chem.,  (1982). 33. S. J. Young, B. Kellenberger, J. H. Reibenspies, S. E. Himmel, M. Manning, O. P. Anderson and J . K. Stille, J. Am.  Chem.  Soc,  1 1 0 , 5744  (1988). 34. C. H. Lindsay and A. L. Balch, Inorg.  Chem.,  2 0 , 2267 (1981).  35. See, for example, (a) S. A. B e s t , T . J. S m i t h a n d R . A. W a l t o n , Inorg.  Chem.,  17, 99  (1978). ( b ) E . H. A b b o t , K. S. B o s e , F. A. C o t t o n , W . T . H a l l a n d J . C . Sekut o w s k i , Inorg.  Chem.,  17, 3240 (1978).  (c) J . R . E b n e r , D . R . T a y l o r a n d R . A. W a l t o n , Inorg. (1976).  14  Chem.,  15, 833  (d) M. Y. Darensbourg, R. L. Mehdawi, T. J. Delord, F. R. Fronczek and S. F. Watkins, J. Am. Chem. Soc, 106, 2583 (1984). 36. P. Espinet, J. Fornies, C. Fortune-, G. Hidalgo, F. Martines, M. Tomas and A. J. Welch, J. Organomet Chem., 317, 105 (1986). 37. C. L. Lee, B. R. James, D. A. Nelson and R. T. Hallen, Organometallics, 3, 1360 (1984). 38. (a) J. R. Fisher, A. J. Mills, S. Sumner, M. P. Brown, M. A. Thomson, R. J. Puddephatt, A. A. Frew, L. Manojlovic-Muir and K. W. Muir, Organometallics, 1, 1421 (1982). (b) R. H. Hill and R. J. Puddephatt, J. Am. Chem. Soc, 105, 5797 (1983) .  (c) B. R. Sutherland and M. Cowie, Inorg. Chem., 23, 1290 (1984).  (d) D. W. Prest, M. J. Mays and P. R. Raithby, J. Chem. Soc, Dalton Trans., 2021 (1982). 39.  A. L. Bakh, L. S. Benner and M. M. Olmstead, Inorg. Chem., 1 8 , 2926 (1979).  40. G . Besenyei, C . L. Lee and B. R. James, J. Chem. Soc, Chem. Com-  mun., 1750 (1986). 41. (a) L. S. Benner, M. M. Olmstead, H. Hope and A. L. Balch, J. Organomet. Chem., 153, C31 (1978). (b) M. Cowie, R. S. Dickson and B. W. Hames, Organometallics, 3, 1879 (1984) .  15  42. G . B e s e n y e i , C . L . L e e , J . G u l i n s k i , S . J . R e t t i g , B . R . J a m e s , D . A . N e l s o n a n d M . A . L i l g a , Inorg. Chem., 26, 3622 (1987).  4 3 . P . G . P r i n g l e a n d B . L . S h a w , J. Chem. Soc, Dalton Trans., 889 (1983).  44. S. P . D e r a n i y a g a l a a n d K . R . G r u n d y , Inorg. Chem., 24, 50 (1985). 4 5 . (a) K . R . G r u n d y a n d K . N . R o b e r t s o n , Organometallics, 2, 1736 (1983). (b) D . L . D e l a e t , D . R . P o w e l l a n d C . P . K u b i a k , Organometallics, 4, 954 (1985).  46. ( a ) J . T . M a g u e , Inorg. Chem., 22, 45 (1983). (b) C . L . L e e , C . T . H u n t a n d A . L . B a l c h , Inorg.  Chem., 20, 2498  (1981).  47. ( a ) A . B l a g g , A . T . H u t t o n , P . G . P r i n g l e a n d B . L . S h a w , J. Chem. Soc, Dalton Trans., 1815 (1984). (b) M . C o w i e a n d S . J . L o e b , Organometallics, 4, 852 (1985). 4 8 . I. R . M c k e e r a n d M . C o w i e , Inorg. Chim. Acta, 6 5 , L 1 0 7 (1982).  4 9 . M . L . K u l l b e r g a n d C . P . K u b i a k , Inorg. Chem., 25, 26 (1986).  16  Chapter 2  E X P E R I M E N T A L  2.1 2.1.1  MATERIALS Solvents  Spectral or analytical grade solvents were obtained from M C B ,  BDH,  Aldrich,  Eastman, Fisher or Mallinckrodt Chemical Co.. Benzene, hexanes and toluene were refluxed with and distilled from sodium/benzophenone  under an atmo-  sphere of N . N,N'-Dimethylacetamide ( D M A ) was stirred over C a H 2  2  for 24 h  prior to fractional distillation under vacuum, and subsequently stored i n the dark. Methanol, ethanol, dichloromethane and acetone were distilled after refluxing w i t h the appropriate drying agents ( M g / I for methanol and ethanol, 2  P 0 5 for dichloromethane, and C a S C u for acetone). Acetonitrile was stored 2  over molecular sieves (Fisher : T y p e 5A, Grade 522, 8-12 mesh) prior to use. Anhydrous diethyl ether and pentanes were used without further purification. A l l solvents were deoxygenated prior to use.  2.1.2  Gases  Purified argon (H.P.), nitrogen (U.S.P.) and hydrogen (U.S.P.) were obtained from U n i o n Carbide Canada Ltd.. Hydrogen was passed through an Engelhard Deoxo catalytic hydrogen purifier to remove traces of oxygen. Hydrogen sulfide ( C P . ) , anhydrous hydrogen chloride and anhydrous hydrogen bromide were  17  obtained from Matheson Gas Co.. All gases, except hydrogen, were used without further purification. D S was prepared by the action of DC1/D 0 (10 mL) on CaS (2 g). The 2  2  resulting gas was first bubbled through D 0 to remove any sulfur oxide impu2  rities and HCl, and then dried over CaCl and P 0 prior to use. 2  2.1.3  2  5  Phosphines and other materials  Reagent grade triphenylphosphine, bis(diphenylphosphino)methane (dpm) and l,3-(diphenylphosphino)propane (dpp) were supplied by Strem Chemicals Inc., while methyldiphenylphosphine was kindly made available by K.Bhangu of this department. All phosphines except dpp were used as such, without further purification, while dpp was crystallized from hot ethanol/hexane mixture under argon. The disulfide of dpm (dpmS ) was prepared by refluxing a mixture of 2  dpm (0.2 gm, 0.55 mmol) and elemental sulfur (S ) (36 mg, 0.14 mmol) in 8  deoxygenated toluene (25 mL) under argon atmosphere for 2 h. The white product which precipitated after the addition of ethanol (50 mL) was then filtered, washed with ethanol (2 x 10 mL) and dried. An attempt to prepare dpm monosulfide (dpmS) employing the above procedure, using one half the amount of elemental sulfur resulted in a mixture containing dpm (~20%), dpmS (~60%) and dpmS (~20%). The purity of all phosphines was checked 2  by P{ ii"} nmr prior to use. 31  1  Benzonitrile (Aldrich), biphenyl (BDH), CaS (Alfa Products) and DC1/D 0 2  (35% (w/w) DC1) were used as such, without further purification. The ligand dibenzylideneacetone (dba) was prepared  1  by the condensation of acetone  (1.45 g, 25 mmol) with benzaldehyde (5.3 g, 50 mmol) in a solution of sodium hydroxide in aqueous ethanol (90 mL); the yellow product was filtered, washed 18  with water (2 x 20 mL) and dried in vacuo. The crude product was recrystallized from hot ethyl acetate. The adduct DMA.HCI was prepared by bubbling anhydrous HCl(g) into 2  DMA(30 mL) to produce a copious white precipitate. The mixture was filtered under Ar, washed well with diethyl ether and vacuum dried. Recrystallization from acetone/diethyl ether afforded colourless, extremely hygroscopic crystals of DMA.HCI. 2.1.4  Palladium Compounds  The palladium, on loan by Johnson Matthey Ltd., was obtained as PdCl . 2  All synthetic reactions, unless specified otherwise, were carried out under an atmosphere of argon, employing Schlenk techniques. 2.1.4.1  Pd(PhCN) Cl 2  2  Trans-dichlorobis(benzonit rile) palladium ( I I ) .  3 , 4  Palladium(II) chloride, PdCl (2.0 g, 11.3 mmol) was suspended in ben2  zonitrile (50 mL) and the mixture warmed to 100°C. After 20 minutes the greater part of palladium(II) chloride has dissolved to give a red solution. This red solution wasfilteredwhile still warm and thefiltratewas poured into hexanes (300 mL). The light yellow product wasfiltered,washed with hexanes and vacuum dried. Yield - 3.9  g(90%)  calculated for C H N Cl Pd; 14  10  C : 44.01, H : 2.69%.  19  2  2  C : 43.84, H : 2.63. Found  2.1.4.2  Pd (dba) .CHCl 2  3  3  Tris(dibenzylideneacetone)dipalladium(0)-chloroform  solvate.  5  Palladium chloride (1.05 g, 5.9 mmol) was added to hot (~50°C) methanol (150 mL), containing dibenzylideneacetone (dba) (4.6 g, 19.6 mmol) and sodium acetate (3.9 g, 47.5 mmol). The mixture was stirred at 40°C to give a reddishpurple precipitate, cooled to complete the precipitation, filtered, and the solid then washed successively with water and acetone and dried in vacuo. T h e precipitate (3.39 g) was dissolved in hot chloroform (120 mL), and filtered to give a deep violet solution. The deep purple needles, which precipitated after the slow addition of diethyl ether (170 mL), were filtered, washed with diethyl ether and dried in vacuo. Yield-2.5 g(85%) calculated for C H Cl 0 Pd S2  43  3  3  2>  C : 60.34, H : 4.19.  Found  C : 60.12, H : 4.10%.  2.1.4.3  Pd Cl (dpm) 2  2  2  Dichlorobis-/x-[bis(diphenylphosphino)methane]dipalladium(I),  6  l a  The title compound was prepared by a procedure slightly modified from that reported. P d ( P h C N ) C l 2  0.53 mmol) and P h P C H P P h 2  2  (0.41 g, 1.01 mmol), P d ( d b a ) . C H C l (0.55 g,  2  2  2  3  3  (0.82 g, 2.1 mmol) were refluxed i n oxygen-free  dichloromethane (50 mL), under a nitrogen atmosphere for 30 min. After being cooled, the resulting red solution was filtered to remove any insoluble materials, and filtrate reduced i n volume to ~ 1 0 mL. T h e yellow-orange product, which precipitated after the addition of diethyl ether (25 m L ) , was then filtered, washed w i t h acetone (2 x 10 m L ) to remove any palladium(II) monomer, and dried i n vacuo.  20  Y i e l d - 1.0 g ( 9 0 % ) calculated for C H P Cl Pd ; 50  44  4  2  C : 57.05, H : 4.21. Found  2  C : 57.45, H : 4.10%. *H nmr 6fgCh 31  : 4.17 p p m (-CH -, q, i _ P  2  = 4 Hz).  H  P { f / ' } n m r i n CD2CI2 showed a single peak at -3.46 ppm. 1  The spectroscopic data for this complex and the others described in the fol7  lowing sections : P d B r ( d p m ) 2 , P d I ( d p m ) 2 , Pd Cl2(dpm)2(/i-S), 8  2  8  2  2  2  2  9  Pd Br 2  2  (dpm) (/i-S), Pd l2(dpm) (/x-S), P d C l ( d p m ) , - and P d B r ( d p m ) , agree 9  9  2  2  10  2  11  10  2  2  with those reported i n the literature.  2.1.4.4  Pd Br (dpm) 2  2  2  Dibromobis-/x-[bis(diphenylphosphino)methane]dipalladium(I),  8  lb  To a solution of Pd2Cl2(dpm)2 (0.23 g, 0.22 mmol) i n dichloromethane (10 mL), a solution of N a B r (0.20 g, 2 mmol) i n aqueous methanol (10 m L ) was added. T h e resulting solution was filtered, a n d concentrated under vacuum until orange crystals were formed. Aqueous methanol was added to complete the precipitation and the product was filtered. Recrystallization from dichloromethane/aqueous methanol followed by vacuum drying yielded an orange-red crystalline product. Y i e l d - 2.35 g ( 9 5 % ) calculated for C H P Br Pd ; 50  44  4  2  2  C : 52.62, H : 3.89. Found  C : 52.20, H : 3.80%. H nmr 8f%£  l  h  : 4.26 ppm (-CH -, q, i 2  P  B  = 4 Hz).  nmr in C D C 1 showed a single peak at -5.5 ppm. 3  2.1.4.5  Pd2l (dpm)2.CH Cl2 2  2  Duodobis-/i-[bis(diphenylphosphino)methane]dipalladium(I)dichloromethane solvate, l c 8  21  The complex was prepared using a procedure similar to that described for P d B r ( d p m ) . T o a solution of P d C l ( d p m ) 2  2  2  2  2  2  (0.23 g, 0.22 mmol) i n dichl-  oromethane (10 mL), a solution of N a l (0.15 g, 1 mmol) in aqueous methanol (10 m L ) was added.  The  resulting solution was filtered and  concentrated  until brownish-violet crystals were formed. Aqueous methanol was added to complete the precipitation; the solid was filtered, washed with acetone (2 x 10 mL)  and dried in vacuo.  Y i e l d -0.27 g ( 9 2 % ) calculated for C^H^ChhPd^  C : 46.39, H : 3.51, I :  19.20. Found C : 46.70, H : 3.60, I : 19.11%.  *H nmr  $ * £ g  P{ H}  nmr  zl  l  2.1.4.6  J  s  : 4.23 p p m (-CH -, q, J _ 2  P  =  H  4 Hz).  in C D C I 3 showed a single peak at -11.3  ppm.  Pd Cl (dpm) (/i-S) 2  2  2  Dichlorobis-/x-[bis(diphenylphosphino)methane]-/x-sulfidodipalladium-  (n),  9  2a  Pd Cl (dpm) 2  mL)  2  2  (0.50 g, 0.48 mmol) was dissolved in dichloromethane (50  and H S gas was bubbled through the solution for 20 min at 20°C; the 2  colour changed from orange-red to brown with accompanying precipitation of brown solid that was completed by gradual addition of diethyl ether (50 mL). The product was filtered, washed successively w i t h acetone (2 x 10 diethyl ether (10 mL)  and dried i n vacuo.  Y i e l d - 0.50 g ( 9 7 % ) calculated for C^H^CliSPdz;  C : 55.36, H : 4.09.  Found C : 55.60, H : 4.27%. 1  H  nmr S££  h  : -CH -, 2.79 p p m ( dq, J 2  4.70 p p m (m, 2 -H  = 13 Hz,  E  nmr i n C D C 1 2  mL),  2  J  P  _  H  H  _ H = 13 E z , J  = 6 Hz).  showed a singlet at 5.50 22  ppm.  P  _  H  = 4 Hz),  2.1.4.7  Pd Br (dpm) (^-S) 2  2  2  Dibromobis-/i-[bis(diphenylphosphino)methane]-/i-sulfidodipalladium(II), 2b H S (50 mL, 1 atm at 25°C) was injected into a Schlenk tube stoppered 2  with a rubber septum, containing a solution of P d B r ( d p m ) 2  2  (0.50 g, 0.47  2  mmol), i n oxygen-free dichloromethane (50 m L ) and allowed to react for 3h; the colour changed from orange-red to brown with accompanying  precipitation  of brown product. The precipitation was completed by the addition of diethyl ether (50 mL); the solid was filtered, washed successively with acetone (2 x 10 mL), diethyl ether (10 m L ) and dried in vacuo. Yield - 0.51 g (98%) calculated for C H^P Br SPd2\ w  A  2  C : 51.13, H : 3.78.  Found C : 51.41, H : 3.96%. 'H  nmr 5*£f  CTj  : - C H - , 2.85 p p m (dq, 3 -H = 13 Hz, 3 .  4.80 p p m (m, 3 -E H  3 1  H  2  = 13 Hz, 3 -  P H  P H  = 4 Hz),  = 6 Hz).  P { H } nmr i n CD C1 showed a singlet at 5.80 ppm. J  2  2.1.4.8  2  Pd I (dpm) (//-S) 2  2  2  Diiodobis-/x-[bis(diphenylphosphino)rnethane]-/x-sulfidodipalladium(n), 2c To a solution of Pd Cl (dpm) (/i-S) (0.25 g, 0.23 mmol), in oxygen-free di2  2  2  chloromethane (25 mL) a solution of Nal (0.30 g, 2 mmol) in aqueous methanol (10 mL) was added. The volume of the solution was reduced to ~10 mL by rotovap to yield brown crystals that were collected, dissolved in dichloromethane (20 mL) and reprecipitated using methanol (50 mL). The precipitate was filtered, washed with methanol (2 x 10 mL) and dried in vacuo.  23  9  Yield - 0.32 g (90%) calculated for C H P hSPd ; 50  44  4  C : 47.34, H : 3.50. Found  2  C : 47.20, H : 3.46%. 1  H nmr Sg$£  la  : - C H - , 3.07 ppm (dq, J . 2  H  = 14 Hz, J _ P  H  f f  = 3 Hz),  4.94 ppm (m, 3 E - H = 14 Hz, Jp-j? = 6 Hz). 31  P^H} nmr in CDC1 showed a singlet at 5.77 ppm. 3  2.1.4.9  PdCl (dpm) 2  Dichloro[bis(diphenylphosphino)methane]palladium(II),  1 0 1 3  6a  To a dichloromethane (10 mL) solution of dpm (0.30 g, 0.78 mmol), a solution of Pd(PhCN) Cl (0.30 g, 0.77 mmol) in dichloromethane (10 mL) 2  2  was added with stirring. The stirring continued for 2h and diethyl ether (50 mL) was added to the yellow solution, which afforded a pale yellow solid. The solid was filtered, and after reprecipitation twice from dichloromethane/diethyl ether, washed with diethyl ether, and dried in vacuo. Yield - 0.35 g (80%) calculated for C sH P Cl SPd; 2  22  2  2  C : 53.46, H : 3.95.  Found C : 53.14, H : 3.90%. *H nmr $  £ g ,  ^P^H}  nmr in CDC1 showed a singlet at -54 ppm.  2.1.4.10  3  :  4.28 ppm (-CH -, t, J _ 2  P  H  = 10.8 Hz).  3  PdBr (dpm) 2  Dibromo[bis(diphenylphosphino)methane]palladium(II),  1 0  6b  T o a dichloromethane solution (10 m L ) o f PdCl (dpm) (0.25 g, 0.45 mmol), 2  a solution o f NaBr (0.20 g, 2 mmol) i n aqueous methanol (10 m L ) was added. T h e resulting solution was filtered, and t h e volume o f t h e solution reduced  24  to ~5 mL in a rotovap.  Aqueous methanol (25 mL) was added to com-  plete the precipitation of the yellow solid. Recrystallization from dichloromethane/methanol, followed by vacuum drying, yielded a yellow product. Yield - 0.23 g (79%) calculated for C H P Br SPd; 25  22  2  C : 46.15, H : 3.41.  2  Found C : 46.00, H : 3.63%. l  H  3 1  nmr f$£  la  : 4.32 ppm ( - C H - , t, 3 _ 2  P  H  = 10.5 Hz).  P { H } nmr in C D C I 3 showed a singlet at -55.8 ppm. 2  2.2  Instrumentation  Infrared spectra were recorded on a Nicolet D X FT-IR spectrometer, as Nujol mulls between Csl plates or as KBr pellets. UV-visible spectra were recorded on a Perkin-Elmer 552A spectrophotometer  with thermostated cell compart-  ments using anaerobic spectral cells of path length 1.0 or 0.1 cm (Fig 2.1). 1  H nmr spectra were recorded on Bruker WP-80, Varian XL-300 or Bruker  WH-400 spectrometers, with tetramethylsilane (TMS) at 8 0.0 ppm as standard.  3 1  P{ H} l  nmr spectra were recorded on a Varian XL-300 (121.4 MHz)  or a Bruker WP-80 (32.3 MHz). The reference for the P{ H) zl  l  nmr spectra  was the signal for triphenylphosphine at -6 ppm (relative to 85% / J 3 P O 4 ) .  11  Chemical shifts are positive in the direction of decreasing field and are reported relative to 85% H3PO4.  All spectrometers were operating in the Fourier trans-  form mode and were equipped with variable temperature control. All samples were sealed under argon, unless otherwise specified. Gas chromatographic analyses were performed on a temperature programmable Hewlett Packard 5890A instrument equipped with a thermal conductivity detector (TCD). A packed molecular sieve column was used with helium  25  as a carrier gas. Mass spectra were recorded on a mass spectrometer (AE1MS9) by the mass spectrometry services of this department. Elemental analyses were carried out by P . Borda of this department.  Procedure for a typical kinetic run  2.3  The kinetics of reaction between the Pd\ complex and H S were monitored 2  spectrophotometrically, under anaerobic conditions by using cells shown in Fig 2.1. In a typical experiment where  PJJ S 2  w  a  s  1 tm, the study was carried a  out as follows: a weighed amount of complex was placed in the quartz side of the cell which was then evacuated and then filled with H2S gas. A slow stream of H S gas was then allowed to flow while a saturated solution of H S (25°C, 2  2  1 atm) in dichloromethane (10 mL) was pipetted into the side-arm flask. The solid and the solvent then were mixed and shaken until a homogeneous solution was obtained. The cell was placed in a thermostated cell compartment and the change in optical density was monitored at a fixed wavelength. The cell was agitated periodically to maintain the "physical equilibrium" of the solution (i.e. to avoid any diffusion problems). For kinetic runs requiring Pjy s values different from 1 atm a slightly mod2  ified procedure was adopted. A weighed amount of solid complex was placed in the cell whilst an appropriate volume of solvent was pipetted into the flask. The solvent was degassed by employing a freeze and thaw static vacuum technique. The solid and the solvent were then mixed and shaken until a homogeneous solution was obtained. The cell was placed in the thermostated cell compartment to allow the solution temperature to equilibrate; when this was  26  100 m m  100 m m  Sidearnv Flask  360 m m  •-Quartz Cell  60 m m  12 m m  F i g u r e 2 . 1 : A n a e r o b i c B p e c t r a l cell u s e d for U V - v i s i b l e spectroscopy.  27  achieved, an appropriate amount of H2S gas or a solution of H2S in the solvent was injected into the cell with the aid of a gas-tight syringe, the experiment then carried out as described above.  2.4  Low temperature nmr experiments with Pd X (dpm)2 and H S . 2  2.4.1  2  2  Reaction of Pd Br (dpm)2 with H S 2  A CD C1 2  2  2  2  (0.6 mL) solution of Pd Br (dpm) , l b , (5 mg) in a 5 mm nmr 2  2  2  tube, stoppered with rubber septum, was degassed employing a freeze and thaw static vacuum technique, and H and P{ H} :  3l  l  nmr spectra were run at  - 7 8 ° C . The sample was then removed from the probe, and H2S (5 m L , l atm, at 25 C) was injected into the cold tube with a gas-tight syringe. The H2S C  gas condensed inside the tube (b.p. - 6 5 ° C ) and the liquid interface (CD2CI2 solution of l b and liquid H2S) turned green. replaced into the - 7 8 ° C probe, and *H and P{ H} 3l  l  The nmr tube was shaken, spectra were run first at  -78°C and then at higher temperatures.  2.4.2  Reaction of P d I ( d p m ) 2 with H S 2  2  2  A CD2CI2 (2.5 mL) solution of l c (20 mg) in a Schlenk tube (10 mL volume) was degassed three times employing the freeze and thaw static vacuum technique. A large excess of H S (~50 mL, 1 atm, 25°C) was then administered 2  into the Schlenk tube, which was then cooled to - 7 4 ° C in a low-temperature slush bath (solid C0 /ethanol), and the system allowed to react for several 2  hours (8 - 20 h).  The initially brownish-red solution of l c , which turned  green over this period, was transferred (at - 7 4 ° C ) to an nmr tube with the aid of a cannula, and H and P{}H} 1  3l  nmr spectra were then run at different  28  temperatures, from -74 to 20°C.  2.5 2.5.1  Interaction of P d B r ( d p m ) 2 with H X 2  2  Room temperature reaction  A solution of l b (3 mg) in oxygen-free CDC1 (5 mL) or C D , in a small 3  6  6  Schlenk tube (5 mL), was degassed three times by the freeze and thaw static vacuum technique. On addition of anhydrous hydrogen bromide gas (50 fiL, 1 atm, 25°C) from a gas-tight syringe, the orange-red solution of l b turned green. UV-visible and H and J  3 1  P{ H} nmr spectra were run immediately l  after the addition of HBr gas, and after several hours when the solution had become pale yellow.  2.5.2  Low temperature reaction  The reaction between the CDCI3 solution of l b and HBr was carried out at low temperature (-40°C) in a nmr tube, stoppered with a rubber septum. The solution was first degassed several times by employing the freeze and thaw technique, then cooled in a low temperature bath (-40°C), and then anhydrous HBr gas was injected into the nmr tube in small increments; after each addition, the *H and P{ if} nmr spectra were run at -40°C. 31  2.6 2.6.1  1  Sulfur abstraction reactions Sulfur abstraction by dpm  In a typical experiment, an equimolar mixture of 2b or 2c and dpm (5 x 10  -2  mmol) in dichloromethane solution (10 mL) were stirred under Ar for 4-10  29  h at room temperature. The solvent was then pumped off and the solid left behind was characterized by *H and P{ H} 31  2.6.2  nmr spectra(see section 5.2.1).  l  D e s u l f u r i z a t i o n of H S 2  The reaction between the complex 2 and H S was carried out in the presence of 2  dpm. The molar ratios of P d to dpm were varied from 1:1 to 1:200 in several 2  experiments, always keeping the H S concentration in large excess. A solution 2  of 2b or 2c (3 mg) and a large excess of dpm (100 mg) in dichloromethane solution (25 mL) were stirred with excess H S (50 mL, 1 atm, 25°C) at room 2  temperature for 4-6 h. The resulting solid was isolated by pumping off the solvent and characterized by H and ^P^H} J  2.7  G a s solubility  nmr spec.tra(see section 5.3).  measurements  The solubility of H S in dichloromethane at specific pressures at 25°C was 2  determined using H nmr spectroscopy. ]  In a typical experiment, a known  volume of CD C1 solution containing either benzene (3 //L) or acetonitrile 2  2  (5 /J.L.) was taken in an nmr tube sealed with a rubber septum. The C D C 1 2  solution was degassed employing the freeze and thaw static vacuum technique. An appropriate volume of H S gas was injected into the nmr tube, which was 2  then shaken well to attain physical equilibrium; the H nmr spectrum was 1  run at 25°C after allowing the solution temperature to equilibrate. From the integral peak intensities, using the benzene or acetonitrile peaks as standard, the H S solubility was readily measured. H S solubility was measured directly 2  2  at various temperatures for the solution initially saturated with H S at room 2  temperature and at 1 atm.  30  2  2.8  References 1. C. R. Conard and M. A. Dolliver, Org. Syn., Coll.  Vol. 2, John Wiley,  Toronto, p.167. 2. I. Thorburn, Ph. D. Dissertation, University of British Columbia, Vancouver, B. C , (1985). 3. M. S. Kharasch, R. C. Seyler and F. R. Mayo, J. Am.  Chem. Soc., 6 3 ,  2088 (1941). 4. J. R. Doyle, P. E. Slade and H. B. Jonassen, Inorg. Synth., 6, 216 (1960). 5. T. Ukai, H. Kawazura, Y. Ishii, J. Bonnet and J. A. Ibers, J.  Organomet.  Chem., 6 5 , 253 (1974). 6. A. L. Balch and L. S. Benner, Inorg. Synth., 2 1 , 47 (1982). 7. A. L. Balch, L. S. Benner and M. M. Olmstead, Inorg. Chem., 18, 2996 (1979). 8. L. S. Benner and A. L. Balch, J. Am.  Chem. Soc, 100, 6099 (1978).  9. G. Besenyei, C. L. Lee, J . Gulinski, S. J. Rettig, B. R. James, D. A. Nelson and M. A. Lilga, Inorg. Chem., 2 6 , 3622 (1987). 10. J . M. Jenkins and J . G. Verkade, Inorg. Synth., 11, 108 (1968). 11. W. L. Steffen and G. J . Palenik, Inorg. Chem., 15, 2432 (1976). 12. G. M. Kosolapoff a n d L. Maier, Organic Phosphorus ed., W i l e y Interscience, Toronto, Vol. 1, 1972, p.130.  31  Compounds,  2  nd  Chapter 3  T H E I N T E R A C T I O N O F H S W I T H Pd(I) D L M E R S 2  3.1  The palladium (I) dpm dimer, P d X ( d p m ) . 2  2  2  The palladium(I) diphenylphosphinomethane dimers, P d X ( d p m ) , [X = CI 2  2  2  (la), Br (lb), I (lc); dpm = P h P C H P P h ] , first reported by Colton et 2  2  2  al., contain an unusually reactive metal-metal bond. The crystal structure of 1  Pd Br (dpm) , Jjb, reveals that the two palladium atoms are connected by a 2  2  2  metal-metal bond, of length  2.669  A.  2  The coordinating geometries about each  metal are approximately square planar, but the two coordination planes(Pd, P, P, Br) are twisted about the B r - P d - P d - B R axis which results in a dihedral angle of 3 9 ° between the planes. In solutions 1 undergoes addition of a number of small molecules, including S, ' R N C , 3  4  2 , 5 , 6  S0 , ' CS , 3  7  2  2  8  CO,  2 , 5 , 6 , 9  and activated acetylenes. Addition of 10  these molecules involves their insertion into the Pd-Pd bond, which breaks, the Pd, Pd separation increasing by ~0.5 A. The insertion of sulfur into the Pd-Pd bond results in the formation of socalled A-frame complexes, Pd X (dpm) (/j-S), 2. Elemental Bulfur and organic 2  2  2  episulfides effect the conversion of 1 to 2. Recent studies in this laboratory 4  have unearthed reaction  (3.1),  which occurs quantitatively in solution at am-  bient conditions for X = CI or Br. Pd X {dpm) 2  2  2  + H S —> Pd X (dpm) {fi 2  2  32  2  2  - S) + H  2  (3.1)  This reaction is of considerable interest because it generates dihydrogen quantitatively from the environmentally hazardous and common industrial byproduct H S. So i t was decided to investigate the kinetic and mechanistic 2  aspects of this reaction in detail. T h e results of these studies are discussed in the following sections.  3.2  Reaction with  D S 2  A solution of l a (25 mg) i n oxygen-free  CH C1 2  2  i n a 10 m L  Schlenk tube  under vacuum was allowed to react with D S (4 mL, 1 atm, 25°C). T h e red2  orange solution of l a turned brown with accompanying precipitation of 2a. The solution was stirred for 30 m i n to complete the reaction. The possible gaseous products evolved ( H , HD, D ) were identified as follows: the contents 2  2  of the Schlenk flask were cooled at l i q u i d - N temperature (to freeze C H C 1 2  2  2  and D S ) , and the mass spectrum of a sample of the gaseous phase was run 2  at low mass range (0-10). T h e spectrum revealed the presence of only D . 2  The brown precipitate of 2 a was isolated after the addition of ether (5 m L ) to complete the precipitation. The isolated solid was dissolved i n C D C 1 and 2  2  the H nmr spectrum was run. The integral intensities of the -CH - proton X  2  peaks (4 H) and those of the phenyl proton peaks (40 H) were compared and found to be i n a 1:10 ratio, reconfirming that there was no deuterium exchange between D S and the -CH - protons of l a i n C H C 1 solution during 2  2  2  the reaction conditions. Thus the H  2  exclusively from the H S reactant. 2  33  2  formed v i a the reaction (3.1) comes  3.3  Kinetics and rate  measurements  A dichloromethane solution of l b is yellow-orange with the following electronic absorptions:  5  A nm  428  10,600  364  17,500  301  23,100  while the dichloromethane solution of P d B r ( d p m ) ( / z - S ) , 2b, is pale yellow 3  2  2  2  with visible absorption bands at 473 nm (1200 M~ cm~ ) l  M  - 1  cm  _ 1  ).  and 348 nm (15200  l  W h e n a dichloromethane solution of l b reacts with hydrogen  sulfide, the visible absorption bands at 428 and 364 nm decrease in intensity while the 473 and 348 nm bands of 2 b grow in intensity, as shown i n F i g 3.1. Anaerobic  spectral cells w i t h path lengths of either 1.0 or 0.1 cm were  used to monitor the reaction between complex l b and H S by observing the 2  disappearance of the 428 n m band i n a UV-visible spectrometer thermostatted  with a well  cell compartment. A l l rates were measured under pseudo-first  order conditions in that the concentration of H S was at least 100 times greater 2  than that of complex l b . T h e reactions were monitored for"up to 2^ - 3 halflives. A typical rate plot and a plot of the data, which analysed for first order in P d j dependence, are shown i n Figs 3.2 and 3.3.  The rates were measured  at palladium concentrations ranging from 8.41 x 1 0 " to 2.23 x 1 0 ~ M, at B  different H S 2  concentrations (7.1 x 1 0 ~  2  t o 5.3 x 1 0  _ 1  3  M) and at different  temperatures (0-35°C). Only one parameter at a time was varied. The dependences of the rate on palladium concentration and hydrogen sulfide concentration were studied at 25° C, i n dichloromethane. 34  T h e solubility  b  350  400  450  500  550  600 nm  Figure 3.1: Visible absorption spectral changes of a dichloromethane solution of Pd Br2(dpm)2 upon addition of H S at 25°C. 2  2  35  1 | .9  r  1  -  Time, s  F i g u r e 3.2: R a t e p l o t for t h e r e a c t i o n b e t w e e n P d B r ( c l p m ) 2 (1.01 x 10 2  a n d H S (0.53 M ) i n C H C 1 2  2  2 )  at 2 5 ° C .  36  2  3  M)  500  1000  1500  2000  2500  Time, s  F i g u r e 3.3: A r a t e p l o t a n a l y s e d for first o r d e r Pd\ 2 5 ° C . ( [ P d * ] = 1.01 x l O "  3  M a n d [ H S ] = 0.53 M ) . 2  37  dependence in C H C 1 2  2  at  of H S i n C H C 1 2  2  2  at 25°C at various H S pressures was determined using the 2  procedure described i n section 2.4, and found to obey Henry's law at least up t o about 1 a t m of H S pressure (Table III-1, F i g 3.4).  Fur-  2  ther, the solubility of H S was calculated to be 1.14 M a t m 2  - 1  or 1.5 x 1 0  - 3  M t o r r . T h e kinetic d a t a for the l b and H S reaction are summarized i n - 1  2  Tables III-2 and III-3, a n d Figs. 3.5 and 3.6.  The reaction is first order  in b o t h [Pd ] and i n H S ; k f, is the pseudo-first order rate constant deter2  0  2  s  mined i n the presence of excess [H S], and equals k [ H S ] , where k is the true 2  2  2  2  bimolecular, second-order rate constant for the reaction.  The temperature  dependence of the rates over the range 0-35°C was investigated at a single p a l l a d i u m concentration (Table III-4). T h e plot of l n ( k / T ) vs. 1/T yields a 2  reasonably good straight line (Fig. 3.7). Values of A H * = 55 ± 5 k J m o l e and A S * = -115 ± 10 J K  - 1  mole  - 1  - 1  were calculated from the slope and i n -  tercept, respectively. Attempts were made to investigate the effect of the added bromide and phosphine on the reaction rate.With these ligands, however, reacton 1.1 took a completely different course; reaction of lb_ with H S in the presence of a 2  five-fold  excess of tetraethylammonium  bromide ( N E t  B r ) resulted i n the -  4  formation of 2 b in only ~ 7 0 % , and several other products were evidenced by 3 1  P { H } nmr and U V - v i s i b l e spectroscopy, especially an unidentified species J  w i t h 8p = 22.2 ppm. A five-fold excess of d p m rendered a catalytic system for the removal of H  2  from H S , and resulted i n the formation of dpm monosulfide 2  along w i t h other p a l l a d i u m compounds (See Ch.5).  38  Table III-1: Solubility of H S i n CH2CI2 at various pressures at 25°C. 2  P# s, atm 0.16 0.22 0.33 0.43 0.46 0.50 0.54 0.58 0.59 0.67 0.78  [ H  2  2  S W /  2  , M  0.20 0.25 0.38 0.50 0.55 0.56 0.62 0.67 0.69 0.74 0.91  Table III-2: Dependence of reaction rate on [Pd ] at 0.53 M [H S] i n C H C 1 at 25°C. !  2  [Pd ]/10- , 0.84 1.81 3.37 4.42 5.13 7.45 8.09 10.0 22.3 4  2  2  W 1 0 - , s8.91 9.05 8.91 8.90 8.92 8.62 9.07 8.84 8.73  M  4  39  1  2  2  F i g u r e 3.4: S o l u b i l i t y of H S i n 2  40  CH2CI2 at v a r i o u s pressures.  T a b l e III-3: CH C1 2  2  D e p e n d e n c e o f r e a c t i o n rate o n [ H S ] a t 1.01 x 1 0 2  - 3  M P d in 2  at 2 5 ° C .  Wio- , s~> 4  [H S]/10- , M a  2  T a b l e III-4:  0.70  1.18  1.3  2.24  1.4  2.80  1.8 2.1  3.01 3.85  2.5  4.01  2.7  4.47  2.8  4.90  3.2  5.25  5.3  8.90  T e m p e r a t u r e d e p e n d e n c e of t h e r a t e c o n s t a n t for t h e r e a c t i o n  b e t w e e n l b (at 1.01 x 1 0  - 3  M ) and H S in C H C 1 . 2  k/10", M " 4  2  2  T-710- , K " 3  1  Mkj/TyiO"  Temp.K  [H S]* M  273  0.50  1.59  3.66  279  0.51  3.61  3.58  288  0.52  6.53  3.47  298  0.53  3.36  -1.21  303 308  0.54 0.55  17.1 20.1  3.30 3.25  -1.19 -1.17  2  2  1  *-  25.5  1  * : solubility measured directly b y H n m r experiments. J  41  -1.44 -1.36 -1.30  1  11  i  r  1  -i  1  1  i  i  r  10  o  I  \ V) O  8 h  0  2.5  5  10  7.5  12.5  15  17.5  20  25  22.5  -4  ;Pd ]/10" , M 2  Figure 3.5: Dependence of reaction rate on [Pd^] at 0.53 M [H S] in C H C 1 2  at 25°C.  42  2  2  0  1  2  3  4  [H S]/10  CH C1 2  2  D e p e n d e n c e of r e a c t i o n r a t e o n [ H S ] at 1.01 x 10 2  at 2 5 ° C .  43  6  , M  2  F i g u r e 3.6:  5  3  M Pd  2  in  -1  T  1  1  1  1  J  I  L  3.4  3.5  1  I ~"  I  I  I  I  L  3.7  3.8  3.9  -1.1  •1.2  -1.3 h  •1.4  -1.5  3  3.1  3.2  3.3  3.6  1/T/10" ,  K"  3  4  1  F i g u r e 3.7: T h e t e m p e r a t u r e d e p e n d e n c e of t h e r a t e c o n s t a n t for t h e r e a c t i o n b e t w e e n l b (at 1.01 x 1 0 "  3  M ) and H S in C H C 1 . 2  44  2  2  Spectroscopic detection of intermediates.  3.4  3.4.1  Reaction between P d B r ( d p m ) 2  2  2  and H  2  S.  The low temperature (—78°C) H nmr spectrum of l b in CD C1 shows the a  2  2  characteristic -CH - proton signal of dpm (8 = 4.26 ppm, q, J P _ H = 4 Hz) 2  along with that of phenyl proton signals (8 between 7 and 8 ppm), which are less informative. The nmr spectra of the l b solution after the addition of H S showed, in addition to the H S signal (0.9 ppm), two additional sets of 2  2  peaks (in the -CH - region 8 = 3.4 ppm, 8 = 3.6 ppm, both broad, 4H, and 2  in the Pd-H region (8 = —8.45 ppm, t,  Jp-jj  = 18 Hz, 1H) attributed to the  formation of a new species in a small amount (~10%), and presumed to be a metal hydride (Figs. 3.8 A - C). Spectra recorded at higher temperatures showed a decrease in the intensity of both sets of peaks up to —65°C, with the gradual formation of Pd Br (dpm) (//-S), 2b, as evidenced by the appearance 2  2  2  of peaks in the -CH - region (8 = 2.85 ppm, J H - H = 13 Hz, J p _ H = 4 Hz, 8 2  = 4.8 ppm, J H - H = 13 Hz, Jp_# = 6 Hz) (Figs. 3.9 A & B). At temperatures above —65°C, only signals due to l_b and 2b were observed. Comparison of the P{ //"} nmr spectrum of l b , and that of l b with 31  1  H S, at —78°C in CD C1 showed the formation of the intermediate hydride. 2  2  2  The spectrum of Jjb with H S had at least four new unresolved broad peaks 2  (8 ~ 5, 8, 19 and 23 ppm) in addition to the single sharp peak of l b at —5.5 ppm (Fig. 3.9). Similar to the *H nmr spectra, the spectrum run at higher temperatures showed a decrease in intensity of the unresolved broad peaks, with the appearance of a new peak (5.8 ppm), that of Pd Br (dpm) (//-S). At 2  2  2  —65°C and above, the nmr spectra showed the presence of only l b and 2b.  45  F i g u r e 3.8: T h e  J  H n m r spectra in  CD2CI2 s o l u t i o n for ( A ) - C H - r e g i o n o f 2  lb; ( B ) - C H - r e g i o n o f l b + H S at - 7 0 ° C a n d ( C ) h y d r i d e r e g i o n o f l b + 2  2  H S at - 7 0 ° C . 2  46  (A)  4.26  F i g u r e 3.9: T h e H n m r s p e c t r a i n C D C 1 J  2  2  ppm  s o l u t i o n of ( A ) - C H - r e g i o n o f l b 2  + H S w a r m e d u p t o r o o m t e m p e r a t u r e a n d ( B ) - C H - r e g i o n of 2b. 2  2  47  -5.5 ppm  19 ppm  8 ppm -78°C  5 ppm  23 ppm  -70°C  5.80 p p m -60°C  -50°C  20° C  F i g u r e 3.10: T h e  S 1  P { H } n m r spectra in C D C 1 1  2  48  2  o f lb a n d H S . 2  These observations, to be discussed later (Section 3.5) are explained by: (i) oxidative addition H S to P d B r ( d p m ) , l b , to form a P d ( H ) ( S H ) inter2  2  2  2  mediate, observable at temperatures below —65°C, and (ii) the formation of Pd Br (dpm) (/i-S), 2b, from the hydride intermediate at temperatures above 2  2  2  ~ -78°C.  Pd Br {dpm) + H S —• Pd Br {dpm) (H){SH) 2  2  2  2  2  2  2  lb  3b —> Pd Br (dpm) (pL - S) + H  Pd Br {dpm) {H)(SH)+ 2  2  2  2  2  2  3b  3.4.2  (3.2)  2  2b  Reaction between P d I ( d p m ) 2  2  2  and H S . 2  Compared to the H nmr spectrum of the complex P d I ( d p m ) , l c , i n C D C 1 , :  2  2  2  2  2  recorded at ~ —78°C, the spectrum of the mixture of l c and H S i n C D C 1 2  showed additional peaks i n the -CH 2  2  region (8 = 5.02 ppm, br singlet, 4H)  2  and  region (8 = —6.05 ppm, br singlet, 1 H) i n addition to the H S peak  in the Pd-H  2  (8 = 0.93 ppm,  br ), again indicating the formation of an intermediate hydride  (Fig. 3.11 A - C). The spectra recorded at higher temperatures ( > —70°C) showed a general decrease i n the intensity of both the 5.02 and —6.05 p p m peaks along w i t h the appearance of a new set of peaks (8 3.07 and 4.97 which are due to the -CH 2  ppm),  protons of P d I ( d p m ) ( / j - S ) , 2c (Fig. 3.12 A & B). 2  2  2  The room temperature spectrum showed the presence of only the Pdl. dimer, l c , and the /i-sulfide, 2c. The  31  P{ H} l  spectrum of the hydride intermediate, which was recorded at  — 74°C i n C D C 1 solutions and more conveniently i n neat H S liquid contain2  2  2  ing a small amount of C D C I 3 , showed two broad peaks (—2.7, —6.7 49  ppm)  in  4.23 p p m  50  (A) -6.05  F i g u r e 3.12: T h e H n m r s p e c t r a i n 1  ppm  CD2CI2 s o l u t i o n of ( A ) l c  — 7 4 C for 8 h ( h y d r i d e a n d - S H r e g i o n ) a n d ( B ) 2jc. 6  51  -f H  2  S k e p t at  addition to a broadened singlet of lc (-11.3 ppm) (Fig. 3.13 A & B). However, as the temperature was increased, the P{ H} 31  spectrum of the intermediate  l  underwent two changes. Firstly, increasing amounts of the intermediate decomposed to form the //-sulfide, 2c, as evidenced from the decrease in the intensity of the intermediate's peaks, along with the appearance of the //-sulfide peak at 5.7 ppm. Secondly, the two peaks of the intermediate coalesced to form a single peak at — 4 . 0 p p m near the vicinity of  —40°C  (Fig. 3.13  C).  As  in case of the H nmr spectra the room temperature spectrum showed the ]  presence of only lc and 2c (Fig 3.14 A & B). These observations are explained i n terms of the same general processes shown above in equation (3.2) for the corresponding bromide system (see section 3.4.1).  3.5  Discussion of kinetic and spectroscopic data  The first-order dependence of rate on both [Pd\] and [H S] can be explained 2  by either of the following mechanisms: (a)  Pd X {dpm) 2  2  + HS  2  Pd X (dpm) (H){SH)  2  2  1  2  (3.3)  2  3  Pd X {dpm) (H)(SH)+ 2  2  Pd X (dpm) (p 2  2  3  2  2  - S) + H  2  (3.4)  2  wherefci,k-i and ki are the rate constants of the individual steps as written. Application of the steady state treatment to the intermediate, P d X ( d p m ) 2 ( H ) ( S H ) , 2  52  2  -11.3 ppm  (A)  (B)  -2.7 ppm 11.3 p p m  -11.3 p p m  (C) 5.7 p p m  -4 ppm  F i g u r e 3.13: T h e " P ^ H } n m r s p e c t r a i n C D C 1  3  o f ( A ) l c at 2 0 ° C ; ( B ) l c +  H S k e p t at — 7 4 ° C for 8 h a n d ( C ) l c + H S k e p t at — 7 4 ° C for 8 h a n d 2  2  t h e n w a r m e d u p t o - 4 0 ° C . ( S i m i l a r d a t a are o b t a i n e d i n C D C 1 . ) 2  53  2  (A)  -11.3 p p m  o.< p p m  5.7 p p m  (B)  F i g u r e 3.14:  The  3 1  P { H } n m r s p e c t r a i n CDC1 3 o f ( A ) l c + H S k e p t at 1  2  ~ - 7 4 ° C for 8 h a n d t h e n w a r m e d t o r o o m t e m p e r a t u r e a n d ( B ) s a m p l e of 2 c at 2 0 ° C . ( S i m i l a r d a t a are o b t a i n e d i n CD2CI2)  54  authentic  3 gives t h e f o l l o w i n g rate l a w .  -d\Pd\]  Rate  d[Pd (fx-S)}  kMPdDlHtS]  2  dt  dt  -+- k  2  That is, Rate =  k'[Pd\][H S] 2  where k^k  2  k' =  If k  2  »  fc_  the rate simplifies to  1}  t i o n 3.3 is r a t e d e t e r m i n i n g . fcifc /fc_i[Pd2][H S] 2  (ki/k-i)  If  k  -f  fc-i  2  fc^Pd^fH^S], ^>  m e a n i n g t h a t t h e reac-  the rate expression becomes  k, 2  or Kfc [Pd2][H S] w h e r e K is now t h e e q u i l i b r i u m 7  2  2  2  f o r r e a c t i o n 3 . 3 , a n d r e a c t i o n 3.4 is r a t e d e t e r m i n i n g .  complete expression for a r a p i d pre-equilibrium determining k  constant  T h e more  ( e q 3.3) f o l l o w e d b y a r a t e  step is  2  k K[Pd\} [H S} 2  R  a  t  e  T  1+  =  w h e r e t h e T s u b s c r i p t i m p h e s t o t a l Td\.  K[H S) 2  T h e s t r i c t l y first o r d e r d e p e n d e n c e o n  H S requires t h a t u p t o [ H S ] = 5.3 x I O 2  2  2  - 1  M ( F i g 3.4), a t 2 5 ° C , K [ H S ] < 2  1,  a n d t h a t 3_b i s n o t d e t e c t a b l e a t t h e c o n d i t i o n s w h e r e t h e H S d e p e n d e n c e was 2  measured. (b) A n e x t r a step w i t h a c c o m p a n y i n g k i n e t i c / e q u i l i b r i u m  parameters is i n -  v o l v e d i f t h e first step i n t h e r e a c t i o n sequence i s f o r m a t i o n o f a n H S a d d u c t : 2  Pd X {dpm) 2  2  + HS  2  2  Pd X (djrm) {H S) 2  2  2  2  ^=h =^ Pd X (dpm) (H S) 0  2  2  2  2  ^ = f c , = * Pd X (dpm) {H){SH) 2  55  2  2  (3.5) (3.6)  Pd X {dpm) {H){SH)+ 2  2  2  -X  Pd X (dpm) {u 2  2  2  (3.7)  - S) + H  2  Consistency with the observed kinetic dependences requires one of the following: (i) the k step is slow and rate determining; rate = a  fc [Pd ][H S]. a  2  2  (ii)fcj,governs the rate determining step, following a rapid K„ pre-equilibrium (k /k_ ) with P d ( H S ) being undetectable; rate = a  a  2  2  (iii) the k step is rate determining, the two  fcfeK [Pd ][H S]. a  2  2  pre-equilibria (k /k_  2  a  a  and  kb/k^b) now again generating undetectable amounts of P d ( H S ) and 2  P d X ( d p m ) ( H ) ( S H ) ; rate = 2  2  2  fc K K [Pd ][H S].  2  2  a  fc  2  2  The simple kinetics measured do not distinguish between the mechanisms of reactions 3.3 and 3.4, and that outlined i n 3.5 to 3.7.  Nevertheless, further  insight into the process, along with information about a reaction intermediate, is gained from the low temperature nmr experiments. The oxidative-addition of H S across the metal-metal bond of 1 would presumably lead to a hydride 2  intermediate of the type 3, w i t h terminal hydride and terminal SH.  3 ( X = CI, a ; Br, b ; I , c)  56  Such oxidative-addition type reactions to the P d X ( d p m ) 2 complexes, in 2  2  which the metal-metal bond acts as a nucleophile, are well established.  11  In  the H S / P d B r ( d p m ) reactions, a hydride intermediate thought to be (3b) is 2  2  2  2  formed at -78°C quite rapidly in a liquid H S interface region and this species 2  rapidly decomposes ( t i < 30 s) to form 2_b at temperatures above ~ - 6 5 ° C . Thus at 0-35°C, the rate determining step will not be decomposition of 3b, (i.e. the k steps of the mechanisms discussed). The rate determining step could 2  be the formation of the hydride 3b (or the H S adduct), and this would be 2  consistent with the non-detection of 3b at ambient conditions. It then seems surprising, however, that 3b is detected at low temperatures. Its formation could presumably result because of one or both of the following factors: (i) the H S addition at low temperatures (below the H S liquefaction tem2  2  perature) produces a very high localized concentration of H S . 2  (ii) optimum temperature conditions prevail so that the oxidative-addition takes place (perhaps because of high H S concentration), while decom2  position of the hydride is slowed down sufficiently to build up the concentration of 3b. It was initially thought that the presence of liquid H S might increase the 2  dielectric constant of the medium, and rates of oxidative-addition of polar molecules are typically enhanced in more polar media.  13  However, dielectric  constant data for C H C 1 and liquid H S at -65°C give e values of 15 and 2  2  2  9, respectively, and thus the changes in dielectric constant are unlikely to be important. Two qualitative observations support the rationale presented above in (i) and (ii). When liquid H S comes in contact with solid l b at ~ - 7 8 ° C a 2  green solution is produced, presumably because of the formation of 3b; based 57  on nmr data, the green solution subsequently yields 2b on warming. Secondly, warming an nmr tube containing successively frozen layers of a solution of l b and H S 2  (liquid N  temperature) generates a green colour i n the upper part  2  of the liquid but only i n a very narrow temperature range (between ~ - 7 0  and  -60°C). The hydride H  nmr  a  signal (8 = -8.9  characteristic of a terminal Pd-H J  1 5  triplet, J P - H  =  18 Hz) is  hydride cis to a phosphine l i g a n d .  non-observation of the 6(Pd-SH) H and -1.5 p p m )  ppm,  nmr  The  14  signal (typically at 8 between 1.5  could be attributed to two possible factors:  (i) the burial of the S-H resonance under the large, broad H S 2  (~0.9  signal  ppm), because the intermediate 3 b is generated only under high  HS 2  concentration. (ii) the S-H proton, which will certainly be a c i d i c  16  may  undergo rapid ex-  change w i t h H S protons thus producing a broad resonance not detected 2  under the experimental conditions. Additional structural information could not be obtained from the  3 1  P{ H} 1  nmr spectrum as it was of poor quality ( F i g 3.9) because of the low concentration of 3 b (~10%). However, the solutions of 3 b should generate a AA' B B ' type  3 1  P { f f } nmr which typically is seen as a pattern centred at four ]  major resonances, and the observed unresolved peaks could result from such 17  a spectrum.  The hydride intermediate for the analogous P d I ( d p m ) / H S 2  2  2  2  system is slow i n forming (~8 h at ~-78°C) but could be obtained at a much higher concentration ( > 5 0 % ) ; the hydride 3 c is much more stable than 3 b but rapidly decomposes at temperatures above -30°C. This further indicates that the oxidative-addition is the rate determining step. 58  It s h o u l d b e n o t e d t h a t f o r m a t i o n  of a p o s s i b l e H S - a d d u c t (i.e.  the  2  K  a  e q u i l i b r i u m i n r e a c t i o n 3.5) is e x p e c t e d to b e f a v o u r e d at lower t e m p e r a t u r e s , b e c a u s e s o l u t i o n reactions o f t h i s t y p e m u s t b e e n t r o p i c a l l y u n f a v o u r a b l e a n d therefore e x o t h e r m i c i f t h e y are t o o c c u r at a l l . T h u s K at l o w e r t e m p e r a t u r e s . intermediate  However, the 2  2  2  Jp_H f°  r  three-bond  w o u l d b e m u c h less t h a n the o b s e r v e d 18 H z w h i c h  values w i t h h y d r i d e cis t o p h o s p h o r u s .  Jp-jj  would be favoured  H n m r d a t a s h o w t h e presence o f a n  hydride and not H S complex formation;  coupling within an P d - S H is t y p i c a l for  J  a  T h e activation parameters ( A H  1  1 4  = 55 K J , A S * = -115 J K  - 1  ) are q u i t e t y p -  i c a l of t h o s e observed for o x i d a t i v e a d d i t i o n r e a c t i o n s at one m e t a l c e n t r e ,  1 8 - 2 0  b u t there are n o t any u s e f u l , c o m p a r a b l e d a t a for d i n u c l e a r s y s t e m s . F o r t h e present P d  2  —> P d ° , f o r m a t i o n of a species s u c h as 3_b necessitates b r e a k i n g  t h e P d - P d b o n d b u t t h e e l e c t r o n i c p r o m o t i o n a l energy  1 8 - 2 0  is n o w o n l y for a  single e l e c t r o n at P d centre a n d w i l l b e less t h a n t h a t r e q u i r e d for 2 e - o x i d a t i v e a d d i t i o n at one ' c o m p a r a b l e ' m e t a l centre; t h e o t h e r factors c o n t r i b u t i n g AH  1  are b r e a k i n g of an S - H b o n d a n d f o r m a t i o n  bonds.  of t h e P d - H a n d  to  Pd-SH  O v e r a l l , t h e a c t i v a t i o n p a r a m e t e r for o x i d a t i v e a d d i t i o n process for  t h e s a m e m o l e c u l e at one o r t w o m e t a l centres m a y t u r n o u t t o b e s i m i l a r .  It  is n o t clear f r o m t h e present s t u d y i f A H * a n d A S * refer t o k j ( e q n . 3.3),  k  or k { , K  ( e q n . 3.5 & 3.6).  a  tion of H  C o r r e s p o n d i n g a m b i g u i t i e s arise i n o x i d a t i v e a d d i -  t o g i v e a d i h y d r o g e n species, n o w t h a t » 7 - H 2  2  a  intermediates have been r e c o g n i z e d .  2 1  2  c o m p l e x e s as p o s s i b l e  O f n o t e , t h e r e a c t i o n of l b w i t h C O t o  give P d B r ( d p m ) ( / j - C O ) i n d i m e t h y l a c e t a m i d e s o l u t i o n , w i t h A H * = 15 K J , 2  2  A S * = -121 J K  2  _ 1  ,  9  is s o m e 10 t i m e s faster t h a n H S r e a c t i o n i n C H C 1 2  2  2  at  c o m p a r a b l e t e m p e r a t u r e s , a n d t h e difference is reflected e n t i r e l y i n t h e A H * v a l u e s ; p r e s u m a b l y , t h e h i g h e r v a l u e for t h e H S s y s t e m results f r o m e n e r g y 2  59  required to break an S-H bond. It would be particularly useful to have activation parameters for the other halide systems; unfortunately the iodide system is photosensitive, but at 25°C the H S reaction is about 10 times slower than for the bromide.  22  2  T h e reac-  tivity trend of 1 toward H S ( X = CI > B r > I) is opposite to that normally 2  encountered for oxidative addition of gas molecules to a single metal centre, where more basic auxiliary ligands promote r e a c t i o n s .  1 8 - 2 0  W i t h i n 1, the P d -  P d bond strength is expected to increase in the order I < B r < CI, the reverse 5  of the trans effect of the halides, and thus the reactivity trend is not domi23  nated by differences in the metal-metal bond strength. Reactivity of 1 toward C O in terms of equilibrium constants is also CI > B r > I, and this is governed by the off-rates that decrease in the reverse order (I > B r > CI), the on-rates being essentially the same; i t has been suggested that the strength of metal9  carbonyl bond i n the product (I < B r < CI) governs the reactivity trend. Such could be the case i n the H S systems, if the k _ i step of the mechanism outlined 2  in eqns. 3.3 and 3.4, or the k_ step of the mechanism given in eqn. 3.5, case a  (ii), become increasingly important  (i.e. these rate constants increase i n the  order kci < k f i < k j ) . r  60  3.6  References  1. R . Colton, H. Farthing and M. J. M c C o n n i c k , Aust. J. Chem., 26, 2607 (1973). 2. R . J. Holloway, B. R . Penhold, R . Colton and M. J. M c C o n n i c k , J. Chem. Soc, Chem. Commun., 485 (1976). 3. A . L. Balch, L. S. Benner and M. M. Olmstead, Inorg. Chem., 18, 2996 (1979). 4. C. L. Lee, G . Besenyei, B. R . James, D . A . Nelson and M. A . Lilga, J . Chem. Soc, Chem. Commun., 1175 (1985). 5. L. S. Benner and A . L. Balch, J. Am. Chem. Soc, 100, 6099 (1978). 6. M. M. Olmstead, H. Hope, L. S. Benner and A . L. Balch, J. Am. Chem. Soc, 9 9 , 5502 (1977). 7. L. S. Benner, M. M. Olmstead, H. Hope and A . L. Balch, J. Organomet. Chem., 153, C31 (1978). 8. M. L. KuUberg and C. P. Kubiak, Inorg. Chem., 25, 26 (1986). 9. C. L. Lee, B. R. James, D. A . Nelson and R. T. Halien, Organometallics, 3, 1360 (1984). 10. A . L. Balch, C. L. Lee, C. H. Lindsay and M. M. Olmstead, J. Organomet. Chem., 177, C22 (1979). 11. R. J . Puddephatt, Chem. Soc Rev., 12, 99 (1983).  61  12. Handbook  of Chemistry  and Physics,  68  t h  Edition, C R C , Boca Raton,  F l a . (1988), p . E 5 0 .  13. R . G . P e a r s o n a n d C . T . K r e s g e , Inorg. Chem., 20, 1878 (1981).  14. S . J . Y o u n g , B . K e l l e n b e r g e r , J . H . R e i b e n s p i e s , S . E . H i m m e l , M . M a n n i n g , 0. P . A n d e r s o n a n d J . K . S t i l l e , J. Am.  Chem.  Soc, 110, 5744  (1988).  15. See, for e x a m p l e : (a) G . B e s e n y e i , C . L . L e e , J . G u l i n s k i , S . J . R e t t i g , B . R . J a m e s , D . A . N e l s o n a n d M . A . L i l g a , Inorg.  Chem., 2 6 , 3622 (1987).  (b) M . R . D u B o i s , M . C . V a n d e r v e e r , D . L . D u B o i s , R . C . H a t t i w i n g e r a n d W. K . M i l l e r , J. Am. Chem. (c) K . O s a k a d a , Y . Y a m a m o t o ,  Soc, 102, 7456 (1980).  A . Y a m a m o t o , Inorg.  Chim.  Acta, 90,  L 5 (1984). (d) R . Y u g o , G . L a M o n i c a , S . C e n i n i , A . Segre a n d F . C o n t i , J. Chem. Soc  A, 5 2 2 (1971).  (e) I. M . B l a c k l a w s , E . A . V . E b s w o r t h , R o b e r t s o n , / . Chem. Soc, Dalton  D. W . H. Rankin and H. E.  Trans., 753 (1978).  16. M . C . J e n n i n g , N . C . P a y n e a n d R . J . P u d d e p h a t t , Chem.  17. NMR,  Comrnun.,  J. Chem.  Soc,  1809 (1986).  Vol 5, E d s . P . D i e h l , E . F l u c k a n d R . K o s f e l d , S p r i n g e r  Verlag,  N e w Y o r k , 1 9 7 1 , p.110.  18. L . V a s k a , Acc. Chem. Res., 21, 120 (1968).  19. J . P . C o l l m a n a n d W . R . R o p e r , Adv. Organomet. 62  Chem. 7, 54 (1968).  20. J . Halpern, Pure. Appl. Chem., 20, 59 (1969). 21. G. J . Kubas, Acc. Chem. Res., 21, 120 (1988). 22. (a) D . Sallin Private  Communication.  (b) A . F . Barnabas, D. Sallin and B. R. James, Can. J. Chem. (submitted). 23. T. G . Appleton, H . C. Clark and L. E . Manzer, Coord. Chem. Rev., 10, 333 (1973).  63  Chapter  T H E I N T E R A C T I O N  4.1  O F H X  (X =  4  CI, Br) W I T H  Pd(I)  DLMERS  Introduction  T h e i n t e r a c t i o n b e t w e e n a n h y d r o u s H C I gas a n d P d ( I ) d i m e r ,  Pd Br (dpm)2 2  2  l b , was d i s c o v e r e d a c c i d e n t a l l j ' , w h i l e t e s t i n g for t h e effect of H X i m p u r i t i e s present i n D S 2  gas (section 3.2.)  o n its r e a c t i o n w ith l b . r  orange c h l o r o f o r m or d i c h l o r o m e t h a n e s o l u t i o n s of l b  T h e yellowish-  t u r n e d d a r k green on  e x p o s u r e t o a n h y d r o u s H C I g a s , en r o u t e t o t h e f o r m a t i o n of t h e p a l e y e l l o w P d ( I I ) m o n o m e r i c species P d ( d p m ) X Approximately Pd  2  ( X = h a l i d e ) , at a m b i e n t  2 m o l e e q u i v a l e n t s of a n h y d r o u s H C I p e r m o l e e q u i v a l e n t  c o m p l e x were r e q u i r e d for t h e c o m p l e t e c o n v e r s i o n of Pd\  2  conditions. of  dimer to a  P d ( I I ) m o n o m e r , as e v i d e n c e d b y n m r s p e c t r o s c o p y . T h e green i n t e r m e d i a t e , i n i t i a l l y f o r m e d , s u b s e q u e n t l y b r o k e d o w n to t h e p a l e y e l l o w P d ( I I ) c o m p l e x e s of the t y p e P d ( d p m ) X , i n a slow r e a c t i o n (t i ~ 30 m i n ) .  The  2  p r o d u c t s c o m p r i s e d a m i x t u r e of P d ( d p m ) C l , P d ( d p m ) B r 2  2  final  Pd(II)  and P d ( d p m ) C l B r  ( F i g 4.1). T h e o x i d a t i v e a d d i t i o n of X  2  ( X = C I , B r , I) t o P d X ( d p m ) 2  2  2  h a d been  s t u d i e d b y B a l c h et a l . T h e r e a c t i o n p r o c e e d e d t h r o u g h t h e o x i d a t i v e a d d i t i o n 1  of X  2  across t h e m e t a l - m e t a l b o n d , r e s u l t i n g i n a green t e t r a h a l o i n t e r m e d i a t e ,  w h i c h w a s d e t e c t e d at l o w t e m p e r a t u r e s before t h e s u b s e q u e n t b r e a k - d o w n t o  64  Pd(dpm)(Cl)(Br) (-54.5, -55, -57.2 k -57.7 p p m )  Pd(dpm)Br (-56.9 ppm)  Pd(dpm)Cl (-55.2 ppm)  2  2  Figure 4.1: T h e P { H } nmr spectra i n CDCI3 of the reaction products of l b and anhydrous H C l ; the A B pattern J = 60 H z is assigned to Pd(dpm)(Cl)(Br). The 6 values for P d ( d p m ) C l and P d ( d p m ) B r are shifted slightly to those given in sections 2.1.4.9 and 2.1.4.10 because of the presence of H C l . 3 1  J  w  2  2  P d ( I l ) monomers (eq 4.1, F i g 4.2).  Pd X (dpm) 2  2  2  + A' — • 2PdX {dpm) 2  2  (4.1)  As the H X reaction w i t h the P d ( I ) dimers seemed to take a similar route, it was decided to investigate the reaction i n more detail to unravel the mechanistic path way of the H X additions.  65  F i g u r e 4.2:  T h e mechanistic pathway of the reaction between l b  ( A d a p t e d f r o m ref.  1).  66  and B r . 2  4.2  Stoichiometry of the reaction and product identification Reaction of P d 2 C l ( d p m )  4.2.1  2  2  with H C l at room temperature  The Pcl(I) complex l a reacted with 2 mole equivalents of HCl, or with the adduct DMA.HCl in D M A , resulting in formation of Pd(dpm)Cl and H . 2  2  Pd Cl (dprn) 2  2  + 2HCI —• 2PdCl (dpm) + H  2  2  la  2  (4.2)  2  6a  The reaction was monitored in D M A as well as in CH C1 by UV-visible, and 2  J  2  H and P{*H} nmr spectroscopy. The nmr spectra are presented in Figs. 4.3 3 1  and 4.4 along with that of an authentic sample of Pd(dpm)Cl , which was 2  prepared from Pd(PhCN) Cl (section 2.1.4.9.). 2  Both H and P{ H} J  3l  l  2  nmr data for l a in CDC1 indicated the disap3  pearance of the l a signals ( H, -CH - protons, 8 = 4.17 ppm, q, Jp_# = J  2  4 Hz; P{ i/}, singlet, —3.46 ppm), and the appearance of the signals of 31  1  Pd(dpm)Cl , ( H, 8 = 4.28 ppm, t, J _ = 10 Hz; ^P^H},  -55.2 ppm)  J  2  P  H  on gradual additions of HCl gas. When the Pd dimer to HCl ratio was 1:2 2  mole equivalents, the l a signals were completely lost. The rapid interaction (ti < 30 s) of anhydrous HCl(g) with l a in CH C1 or CHC1 solutions at 2  2  3  room temperature resulted in the appearance (UV-visible spectra) of a new band at 320 nm at the expense of the 416 and 347 nm bands of la. A similar reaction was observed in D M A solutions between l a and DMA.HCl but at a much slower rate (ti ~ 45 min). v  2  The gaseous product, dihydrogen, was detected and identified by gas chromatography by comparison with authentic H gas. A packed molecular sieve 2  67  4.17 ppm  (A)  (B)  4.17 ppm  4.28 ppm  (C)  Figure 4.3: The H nmr spectra (-CH - region) in CDC1 solution at 20°C of (A) la; (B) l a + HCl(g) (~3:l) and (C) l a + HCl(g) (1:2). J  2  68  3  (A)  -3.46  ppm  -3.46  ppm  I*  (B)  -55.2 ppm  (C)  F i g u r e 4.4:  -55.2 ppm  The  3 1  P { ' H } n m r spectra in C D C 1  3  s o l u t i o n at 20°C of ( A )  ( B ) l a + H C l ( g ) ( - 3 : 1 ) a n d ( C ) l a + H C l ( g ) (1:2).  69  la;  column was used in a Hewlett Packard 5890A instrument equipped with a thermal conductivity detector (TCD); a retention time of 1.05 min was measured for the gaseous product and authentic H (Fig 4.5). A n attempt to detect 2  reaction intermediates at low temperature (—78°C), akin to C l addition to 2  la  1  (cf. Fig 4.2), was not successful.  4.2.2  R e a c t i o n of P d B r ( d p m ) w i t h H B r at r o o m t e m p e r a t u r e 2  2  2  As summarised in section 4.1 and shown in section 4.2.1, the chloroform and dichloromethane solutions of l a or l b required ~2 mole equivalents of H X per mole of palladium complex for reaction. This is readily rationalized in terms of (i) oxidative-addition of a mole of, for example, HBr to l b leading to a palladium hydride product, 4b: Pd Br (dpm) 2  2  + 2HBr  2  • Pd Br (dpm) (H){Br) 2  2  (4.3)  2  lb  4b  (ii) the reaction of 4b with a second mole of HBr leading to a tetrabromopalladium(II) product, 5_b, and hydrogen (H ): 2  Pd Br (dpm) {H)(Br) 2  2  + HBr  2  > Pd Br (dpm) 2  4  4b  2  + H  2  (4.4)  5b  and (iii) the break-down of 5b to the monomeric Pd(II) species:  Pd Br (dpm) 2  4  2  — • 2PdBr (dpm) 2  5b  (4.5)  6b  Evidence for the pathways of reactions (4.3) - (4.5) was obtained from the 70  F i g u r e 4.5: T h e gas chromatograms of ( A ) the gaseous products evolved in the reaction of l a 4- 2 HCl(g) i n D M A ; (B) the gaseous products evolved i n the reaction of l b + 2 HBr(g) i n C H C 1 and (C) authentic dihydrogen gas. 2  2  P d B r ( d p m ) / H B r system. T h e reaction of l b with H B r i n CDC1 was mon2  2  3  2  ( F i g 4.6).  itored by *H nmr, P { f f } nmr and UV-visible spectroscopy 3 1  1  Wavelength(A) n m  Figure 4.6: Visible absorption spectrum of dichloromethane solution of Pd Br2(dpm) upon addition of anhydrous H B r at 25°C, as a function of time; the P d B r ( d p m ) ( A = 364, 428 nm) 'instantly' gives P d B r ( d p m ) ( A = 360, 600 nm) that slowly converts to P d B r ( d p m ) ( A = 338, 380 nm). 2  2  2  2  2  m a a ;  2  2  4  2  m 0 i E  m o i e  nmr spectra at 20° C are presented in figures 4.7 and 4.8, along with the spectrum of an authentic sample of PdBr (dpm), 6b, which was prepared from 2  PdCl (dpm) (see section 2.1.4.10). In the * H nmr spectrum, two sets of peaks, 2  a singlet (6 — 4.63 ppm) and a triplet (6 = 4.31 ppm, Jp_jy = 10 H z ) appeared in the - C H - proton region, immediately on addition of anhydrous hydrogen 2  bromide gas to l b in solution; the signal due to the - C H - proton of the dpm 2  of l b (6 = 4.26 ppm, q, Jp_jj = 4 H z ) had disappeared. The singlet at 4.63 72  ! (C)  (A)  J  4. 31 p p m  4.26 ppm  1  i  !  (D)  (B)  4 31 p p m  4.31 p p m  JI  4.63 p p m  Figure 4.7: The *H nmr spectra (-CH - region) in CDC1 solution at 20°C of (A) lb; (B) l b + HBr(g) after 15 min.; (C) l b + HBr(g) after 6 h and (D) authentic sample of PdBr (dpm). 2  2  73  S  (C)  (A)  -56.9 ppm  -o.o ppm  (D)  (B) -56.9 p p m  -56.9 p p m  5.2 p p m  Figure 4 . 8 : The P^H} nmr spectra in C D C 1 solution at 2 0 ° C of ( A ) l b ; (B) l b 4 HBr(g) after 15 min.; ( C ) l b + HBr(g) after 6 h and (D) authentic sample of PdBr (dpm). 8 1  3  2  74  ppm  then lost its intensity slowly ( t i ~ 30 min), while the triplet grew in  intensity as the reaction proceeded. A singlet appeared at 6 5.2 p p m in the 31  P{ H}  spectrum nmr along with a low intensity singlet at —56.9 ppm. T h e  l  high field singlet (6 = —56.9 ppm) The  J  H and  31  P{*H}  grew in intensity as the reaction proceeded.  nmr spectra (Figs. 4.7 C, D , 4.8 C &: D) show that the  identity of the final palladium product is P d B r ( d p m ) . 2  The  J  H (6 = 4.63 ppm)  and  3 1  P { / / } n m r data along with absence of 1  high field resonance in the hydride region show that the intermediate is 5 b rather than 4b. B o t h the *H and  3 1  P { 7 7 } nmr 1  data are in good agreement  with those of 5_b observed by Balch et al., on reacting l b with B r 1  solution at -40°C { E: 6 = 4.6 p p m and l  3 1  P { i ? } : 6 = 4.90 1  2  in  CDCI3  ppm).  The gaseous product dihydrogen formed during the reaction was  detected  as described i n section 4.2.1 for the l a / H C l reaction (Fig 4.5).  4.2.3  Low temperature spectroscopic studies of the reaction between l b and H B r .  A low temperature titration between a CDCI3 solution of lb and anhydrous HBr 3 1  gas was carried out at — 40°C, and the changes monitored  P { i / } nmr J  with *H and  spectroscopy, (section 2.5.2.). A d d i t i o n of up to 1 mole equiv-  alent of anhydrous H B r to l b in solution resulted in the formation of a new species, a green hydride intermediate with *H nmr signals at 6= 4.60 p p m (br, s, 4 H) and at 6= -8.9 ppm  (br, s, 1 H) (Figs 4.9 A & 4.10 A). Further addition  of H B r gas resulted in the depletion of the hydride intermediate, as evidenced by the decrease in the intensity of hydride intermediate's *H nmr signals, with concomitant formation of the tetrabromo intermediate, P d B r ( d p m ) . 2  75  4  2  4.26 p p m  (A)  lb  4.60 p p m Hydride  4.60 p p m 4.63 ppm  (B)  Hydride Pd Br (dpm) 2  4  2  4.31 p p m <-PdBr (dpm) 2  (C)  Figure 4.9: The *H nmr spectra (-CH - region) in CDC1 solution at -40°C of (A) l b + HBr(g) (2:1); (B) l b + HBr(g) (1:2) after ~15 min and (C) l b + HBr(g) (1:2) after ~30 min. 2  76  3  (A)  l - PP 8  m  e  W \  4  -  4  2  —>  31 p p m  1  4.63 p p m  2  m  L  (B)  Pd Br (dpm)  9  ^ l^-PdBr (dpm) 2  J  4 .31 p p m  (C)  J  I  Figure 4.10: The *H nmr spectra in CDC1 solution at -40°C of (A) l b + HBr(g)(l:l), the high field region after ~ 2 min; (B) l b + HBr(g) (1:2) after 60 min, - C H - region and (C) l b + HBr(g) (1:2) after 6 h, - C H - region. 3  2  2  77  The tetrabromo intermediate slowly broke down at low temperature to Pd(II) monomer or more rapidly if the solution was warmed up to room temperature. nmr spectrum of a solution of l b containing 2 mole equiva-  The P{ H} 31  X  lents of H B r (analogous to Fig 4.9 B) had signals at 8p = -55.6 ppm (sharp, s) and at Bp — 6.2 ppm (br, s) (Fig 4.11 A ) . The high field signal corresponds to that of PdBr (dpm) ( see section 2.1.4.10). The low field signal is not eas2  ily assigned but could arise from the time averaging of various signals ( for example, Pd Br (dpm)2 and Pd2Br (dpm) (H)(Br) species.) Further, in the 2  4  2  2  presence of excess H B r , the 8 = 6.2 ppm peak shifted to the low field side P  and is seen as a multiplet, while the corresponding shift in the high field signal was negligible (Fig 4.11 B & C ) .  4.3  Discussion  The H B r / i b reaction proceeds stepwise and the changes taking place at the low temperatures are depicted as follows:  fast  Pd Br (dpm) 2  2  + HBr ^  2  2  l b . yellow orange  2  2  2  4b, green  Pd Br (dpm) (H)(Br) 2  (4.6)  Pd Br (dpm) (H)(Br)  + HBr ^  2  Pd Br (dpm) 2  4  2  + H  2  (4.7)  5b, green  4b. green slow  Pd Br (dpm) 2  4  2  2PdBr (dpm) 2  6b, pale yellow  5b, green 78  (4.8)  -55.6 p p m <-PdBr (dp>m) 2  (B)  :  .8 ppm  -55.7 ppm  -55.8 ppm  (C)  8 ppm  Figure 4.11: The P{ H} nmr spectra in CDC1 solution at -40°C of (A) l b + HBr(g) (1:2) after ~15 min; (B) l b + HBr(g) (1:5) after ~20 min and (C) l b + HBr(g) (1:10) after ~25 min. l b + HBr(g) (2:1) after ~15 min, the P{*H} nmr spectra in CDC1 shows peaks at -55.6 ppm (sharp, s) and 5.4 ppm (br, s). 31  J  3  31  3  79  The first mole of H B r oxidatively adds across the P d , P d bond, and leads to the formation a transient palladium hydride intermediate observable at low temperatures (-40°C) by nmr spectroscopy. Such a hydride intermediate could have any one or more of the following structures: (i) A face-to-face bridged structure as observed in the Rh(I) dimers Rli2(dpm)2(C0) C1 2  and Rh (dam)2(CO) Cl2, and i n the Pd(II) dimers P d ( d p m ) 3  2 2 )  2  2  2  Cl (CH- ) , Pd Cl [Bu P(CH2) PBu ]2, 4  2  3  2  2  4  2  7  5,6  2  2  and P d C l 4 [ B u P ( C H 2 ) P B u ] 2 . ' 5  2  2  (ii) A /i-hydrido /j-bromo bridged structure commonly observed  10  6  2  i n doubly  bridged dimers . 7  (iii) A d i m e r having a A - f r a m e  structure, w i t h a hydrido bridge,  80  as f o u n d  in many P t and P d dimers with dpm as the bridging ligand. C1 (H)] , [ P t ( d p m ) M e ( H ) ] , and [ P d ( d p m ) M e ( H ) ] +  8  +  2  2  2  9  2  2  2  2  + 4  [Pt (dpm) 2  2  are examples of  cationic complexes exhibiting A-frame structures with bridging hydride.  +  Y"  The observed H (broad -CH - signal and hydride signal) and P { H } (broad J  3 3  1  2  singlet) nmr spectra of 4 b can be accounted for by any one of the above structures or by two or more of the structures i n equilibrium with each other. The reaction of the second mole of H B r with the hydride intermediate leads to the generation of H  2  gas along with formation of a tetrabromide intermedi-  ate. The presence of a sharp singlet i n both the *H and P { H } nmr spectra 3 1  J  indicates a more symmetric structure persumably with equivalent phosphorus atoms and methylene protons.  A face-to-face bridged structure, a dibromo  bridged structure, or a /i-bromo bridged A - frame structure with rapidly exchanging methylene protons, would give the observed H and P { H } nmr 1  3 1  J  spectra. T h e subsequent break down of the tetrabromo intermediate, 5b, to Pd(II) monomer, 6b, is a much slower process ( t i  ~ 30 m i n at 20°C) than  that of the corresponding iodide species, P d I ( d p m ) ( U = 6 m i n at 15°C). 2  4  1  2  The breakdown of 5b, if it exibits the face-to-face dimer structure, would proceed simply through the scission of P d - P bonds. O f interest, the complexes of  81  the type P d C L ; [ B u P ( C H ) P B u ] 2  2  2  n  2  2  (n = 7, 10),  5,6  in which the P d centers are  well seperated by the long methylene chains of the bridging bisphosphine Ligands, are found to be indefinitely stable i n solution; obviously, i n these cases, the formation of a halide bridge between the metal centers is not possible and this indicates that the formation of a halogen bridge between the metal atoms is a prerequisite for the scission of a P d - P bond. Thus the breakdown of 5_b is likely to take place through the structures (ii) and /or (iii). If the reaction between l a and HCI proceeds through the above mechanism, then at low temperatures the reaction would generate the transient intermediates P d C l ( d p m ) ( H ) ( C l ) and P d C l ( d p m ) , analogous to the l b 2  2  2  2  4  2  system. T h e tetrachloro intermediate has been observed i n the oxidative addition of C l to l a at low temperatures (-40°C) i n C H C 1 2  2  solutions. Failure 1  2  to detect any intermediate i n the present work even at -78°C indicates that the H C I / l a reaction proceeds either through a mechanistic pathway i n which P d C L i ( d p m ) is not formed or, more likely, the tetrachloro species is formed 2  2  but its subsequent breakdown to the monomer is fast (perhaps catalysed by HCI) and no longer rate determining as i n the reaction between l a and C l 2  82  4.4  References 1. C. H. Lindsay and A. L. Balch, Inorg. Chem., 20, 2267 (1981).  2. M. Cowie and S. K. Dwight, Inorg. Chem., 19, 2500 (1980). 3. J. T . Mague, Inorg. Chem., 8 , 1975 (1969). 4. S. J. Young, B. Kellenberger, J. H. Reibenspies, S. E. Himmel, M. Manning, O. P. Anderson and J. K. Stille, J. Am. Chem.  Soc, 110, 5744  (1988). 5. N. A. Al-Salem, H. D. Empsall, R. Markham, B. L. Shaw and B. Weeks, J. Chem. Soc, Dalton Trans., 1972 (1979). 6. B. L. Shaw, i n Catalytic  aspects of metal phosphine  complexes, E d i t e d  by C. Alyea and D. W. Meek, Advances i n Chemistry Series 196, Am. Chem. Soc, Washington, D. C. (1982), Ch.6. 7. See, for example: C. Bianchini, C. Meali, A. Meli and M. Sabat, Inorg. Chem., 25, 4617 (1986). 8. M. P. Brown, R. J. Puddephatt, M. Rashidi and K. R. J. Seddon, Inorg. Chim.  Acta, 23, L27 (1977).  9. M. P. Brown, J. R. Fisher, S. J. Franklin, R. J. Puddephatt and M. A. Thomson, i n Catalytic  aspects of metal phosphine  complexes, Edited b y  C. A l y e a and W. Meek, Advances i n Chemistry Series 196, Am. Chem. S o c , Washington, D. C. (1982), Ch.13.  83  Chapter 5  SULFUR TRANSFER  5.1  REACTIONS  Introduction  The key factor in transforming the stoichiometric reaction 3.1 into some useful type of catalytic process lies i n the successful regeneration of 1, by the removal of the bound // -sulnde ligand. In principle, numerous strategies could 2  be applied (scheme 5.1) for the sulfur removal, because // -sulfur exhibits both 2  nucleophilic and electrophilic nature in transition metal c o m p l e x e s .  Pd I  2  -  + H S 2  Pd S + H 2 2  1-5  (3.1)  2  Pd  2  + S  2  + S0  2  +  1  Pd  2  1 Pd  ES/NS  1 Pd  2  = Pd X (dpm) 2  2  2 )  I , X = C l ( a ) , B r ( b ) , 1(c);  P d S = Pd X (dpm) (/i-S), 2 a - 2c; P d S 0 2  2  2  2  2  2  = Pd X (dpm) (//-S0 ); 2  2  2  [O] = oxidizing agent such as m-Cl-C6H4C(0)0 H; 2  N  = nucleophilic S acceptor and E = electrophilic S acceptor. Scheme 5.1  84  2  Successful regeneration of 1. could lead to a catalytic process that would desulfurize H2S and generate dihydrogen The interaction between S 0  2  gas.  and 1 leads to the formation of the known  A-frame complex Pd X2(dpm)2(/i-S02), which loses SO2 reversibly and thus 6  2  has a much weaker Pd-S bond than that of 2; oxidation of 2 thus presented a plausible pathway to regenerate 1, and this was accomplished but the S 0  2  using peracids,  7  co-product i n the net catalytic reaction (equation 5.1) makes the  process relatively unattractive. H S + 2RC(0)0 H—>H 2  2  + S0  2  Photolysis of 2 has been considered  2  8  + 2RC0 H  (5.1)  2  to lead to the possible regeneration of  1 along with elemental sulfur, which would precipitate out i n solvents like dibutylphthalate of low sulfur solubility. Finally fi -S could perhaps be ab2  stracted by transferring i t to a sulfur-accepting moiety.  B o t h electrophilic  ( H , R ) and nudeophilic ( P R , P A r , C N " ) reagents offer possibilities. +  +  3  3  Of the above methods outlined for the sulfur removal, the oxidation with peracids is the only successful route utilized so far for the regeneration of 1.. The oxidation of the /^-sulfide proceeded through the formation of an fi-SO isolable intermediate, which was subsequently oxidized to the fi-S0 which i n turn lost SO2 spontaneously  2  complex,  at room temperature to yield 1 ( F i g  5.1). Some attempts to dislodge the /i -sulfide by 'non-oxidative' routes (i.e. 2  to sulfur oxides) are discussed i n the following sections.  85  Pd Xj(dpm) 0x-S) +H,  Pd^dpm).  2  CH,CI,  2  so, 30X H,0„ 25'C CH,Cli/MeOH  PdjX^dpm^Oi-SO,)  PdjXj(dpm)jOt-SO)  m-CI-C,H C(0)0,H, -60*C 4  Figure 5.1: The schematic representation of the regeneration of 1 from 2. by the oxidation of the ^-sulfide to S0 2  86  5.2  Sulfur a b s t r a c t i o n reactions  5.2.1  Sulfur a b s t r a c t i o n by phosphines  Co-ordinated sulfur atoms are effectively removed as SPPh , by reacting with 3  PPh .  9,10  3  . Attempts to regenerate l a by reacting 2_a_ with excess PPh were 3  unsuccessful; a slow reaction in CH C1 at 40°C destroyed much of the 2a but 2  2  l a was never recovered in more than 20% yield. In the present work both 2b 7  and 2_c showed inertness toward /i -sulfide abstraction by PPh , and indeed 2  3  could be recovered back unchanged in good yields (>90%). In an attempt to abstract the /x-sulfide ligand, the bisphosphines dpm and dpe and the 2  monophosphine PPh Me were also tried. 2  The reaction between 2b or 2c and dpm in CH C1 at 2 0 ° C generated Jjb 2  2  in ~ 7 5 % yield or lc quantitatively after ~ 6 h stirring. Interestingly, in each case (eq 5.2), dpm monosulfide (nmr : H, 8 — 3.32 ppm, dd, Jp_# = 1 Hz, J  J p ( S ) - H = 12-8  Hz ; and P{ #} 8 = 31  ]  -28  ppm, d, ; 40 ppm, d, J  P  _  P  = 76  Hz) was the only phosphorus-sulfur compound formed and the nmr data are in excellent agreement with literature data.  11  P<z Y(<zprn)(^ — 2J  2  2  • Pcf X (^pm) -f dpmS  S) -f dpm  2  2  2  2  (5.2)  1  The reactions between 2b or 2c with dpe or PPh Me were, like the PPh 2  3  reactions, unsuccessful for the regeneration of l b or l c , respectively. In the dpe case, l b or l c was generated in ~50% yield along with numerous(from H J  & P{ H}), as yet unidentified, Pd complexes. The PPh Me reaction did not 31  V  2  regenerate any ljb or l c , but much of the respective 2b or 2c was destroyed, presumably by the break down of the Pd and ^-sulfide dimers. 2  87  T h e i n a b i l i t y of P P h  3  to m o b i l i z e sulfur f r o m 2 b / 2 c i n d i c a t e s t h a t either  2 b / 2 c is t h e r m o d y n a m i c a l l y s t a b l e w i t h respect to t h e f o r m a t i o n of l b / l c a n d S P P h , or else t h e r e a c t i o n is t h e r m o d y n a m i c a l l y f a v o u r a b l e b u t k i n e t i c a l l y dif3  ficult.  T h e facile f o r m a t i o n of d p m m o n o s u l f i d e i n r e a c t i o n (5.2)  the P P h  3  indicates that  r e a c t i o n does not take p l a c e b e c a u s e o f k i n e t i c reasons. T h e specific  transfer o f s u l f u r to one p h o s p h o r u s a t o m of t h e d p m ( d p m d i s u l f i d e f o r m a t i o n was facile i n a r e a c t i o n between d p m S a n d e l e m e n t a l sulfur(S8), a n d i n a d p m r e a c t i o n w i t h s u l f u r (1:|), a l o n g w i t h some d p m S ) suggests t h a t the r e a c t i o n may involve a dangling (monodentate)  d p m intermediate, w i t h perhaps the  b i n d i n g of d p m at one e n d b e i n g necessary d u r i n g the sulfur transfer.  Further,  such a d a n g l i n g d p m l i g a n d w o u l d severely w e a k e n t h e P d - S b o n d b e c a u s e t h e / / - s u l f i d e w o u l d n o w b e trans to t w o l i g a n d s ( B r a n d the P a t o m of t h e a d d e d d p m ) w i t h different t r a n s - i n f l u e n c e s .  12  T h e r e a c t i o n m a y p r o c e e d t h r o u g h the  f o l l o w i n g p l a u s i b l e m e c h a n i s m , as s h o w n i n F i g u r e 5.2;  t h e b r o m i n e at the  P d metal being attacked could alternatively dissociate, and then  finally  socdate, as b r o m i d e .  carried out  Further, preliminary kinetic investigations  1 3  reas-  subsequent to t h i s w o r k , i n d i c a t e t h a t the r e a c t i o n b e t w e e n 2 c a n d d p m is w e l l b e h a v e d , as e v i d e n c e d f r o m U V - v i s i b l e s p e c t r o s c o p y a n d shows a  first  order d e p e n d e n c e o n b o t h [ P d ] a n d [dpm] i n a c c o r d a n c e w i t h t h e p r o p o s e d 2  m e c h a n i s m i f t h e first step is r a t e - d e t e r m i n i n g .  5.2.2 The  S u l f u r abstraction b y organics  successful a b s t r a c t i o n o f / ^ - s u l f i d e by d p m s i g n a l l e d searches for o t h e r  w a y s o f a b s t r a c t i n g t h e b o u n d s u l f u r f r o m 2, b e c a u s e t h e a b s t r a c t i o n of fi 2  sulfide b y d p m is u n l i k e l y to b e u n i q u e . B e n z o t h i o p h e n e a n d d i b e n z o t h i o p h e n e derivatives are q u i t e i n e r t t o w a r d h y d r o d e s u l f u r i z a t i o n (i.e. r e m o v a l of s u l f u r  88  Br — P d  P d — Br.  +  P  P  F i g u r e 5.2: T h e p r o p o s e d m e c h a n i s t i c p a t h w a y f o r t h e a b s t r a c t i o n of s u l f u r b y bis(diphenylphosphino)methane  from  2.  89  as H S), indicating a stable carbon-sulfur framework. Thus, sulfur abstraction 2  from 2 was considered likely to occur if it led to the formation of benzothiophene or dibenzothiophene derivatives,and so biphenyl and styrene were judged to be likely molecules for abstraction of the bound /z-sulfide from 2. The reaction between 2_c and styrene was unsuccessful, however, for the sulfur abstraction. With diphenyl a small amount (~ 15%) of l c was regenerated from 2c at room temperature in 2 h. A much higher conversion (~45%) was effected in refiuxing toluene in 2 h. From the  3 1  P{ H} spectrum, the l  reaction appeared to be clean, showing the presence of only l_c and 2_c. The organic sulfur product formed remains to be identified. 5.3  The desulfurization of H S 2  As discussed in section 5.1, the coupling of reaction 3.1 and reaction 5.2 should yield a process which catalytically desulfurizes H S and result in the generation 2  of H and dpmS, eq 5.3. 2  HS 2  + dpm  • H -+• dpmS  (5.3)  2  Such proved to be the case. In a blank reaction containing no Pd complexes, dpm was recovered quantitatively, unchanged after reacting with H S(excess) 2  in CH C1 at 25°C even after 2 days. However, in the presence of a small 2  2  amount of 1 (b or c) (Pd : dpm = 1 : 200, CH C1 , 25°C, 8h) dpm was cat2  alytically  2  2  converted to dpmS, indicating the generation of an efficient, catalytic  system for desulfurization of H S (Figs. 5.3 and 5.4). Of interest, on closer 2  examination, the desulfurization of H S perhaps proceeds through a route dif2  ferent from the one predicted by the coupling of the reactions 3.1 and 5.2. Catalysis via these reactions should generate (finally or during the catalysis) 90  "1  (A)  dpmS  l. i  i  I  i  i  40  I  3d  i  .  11  ..  i i  i  i  i  I  i  i  20  i  I>  i  i  I  i  10  .  I 0  i  i  i i  I  i  i  i  -]0  i  I  i  i  i  -20  i  I  i  -30  i  i  -36 ppm  (B)  i  II  II  I I I | I I I I | I I I I | I I I I | I I I I J I I I I | I I I I J I I I I |  35  30  25  20  15  10  5  0  -5 P P ™  Figure 5.3: The P{*H} nmr spectra in CDC1 solution at 20°C of (A) the reaction product of l c and H S in the presence of 20 fold excess dpm after 2 h; (B) the expanded region of (A) between -5 and 36 ppm. n  3  2  91  I 30  I I I I  I  I I I I  25  I  I I I I  20  I  I I I I  15  I 10  I I I I  I 5  I I I  I I  0  I I I I  I  I  -5 P P  m  Figure 5.4: The P{ H) nmr spectra in CDC13 solution at 20°C of (A) the reaction product of lfc and H S in the presence of 20-fold excess dpm after 2 h, the dpm signal had completely disappeared after 8 h. (B) the expanded region of (A) 3 1  l  2  92  either l ( b or c) in the system if dpm was in excess, or 2 ( b or c) if H2S was in excess. However, in desulfurization reactions catalyzed by 1 species neither 1 nor 2 was detected. Instead, a few unidentified palladium products, presumably dpmS substituted derivatives of 1 and/or 2, were detected in the P{ 7J'} nmr spectra (Figs. 5.3B and 5.4B). .  31  1  93  5.4  References  1. C. J . Casewit, R. C. Haltiwagner, J. Noordik and M. Rakowski DuBois, Organometallics,  4, 119 (1985).  2. (a) R. G. W. Gingerich and R. J. Angelici, J. Am.  Chem.  Soc, 1 0 1 ,  5804 (1979). (b)R. J. Angelici, Acc. Chem. Res., 21, 387 (1988). 3. C. M. Bolinger, T. B. Rauchfuss and S. Wilson, J. Am.  Chem.  Soc,  4. M. G. B. Drew, P. C. H. Mitchell and C. F. Pygall, J. Chem.  Soc,  104, 7313 (1982).  Dalton  Trans., 1213 (1979).  5. C. P. K u b i a k and R. Eisenberg, Inorg. Chem., 19, 2726 (1980). 6. A. L. Balch, L. S. Benner and M. M. Olmstead, Inorg. Chem., 18, 2996 (1979). 7. G. Besenyei, C. L. Lee, J . Gulinski, S. J . Rettig, B. R. James, D. A. Nelson and M. A. Lilga, Inorg. Chem., 26, 3622 (1985). 8. B. R. James, Personal  Communication.  9. K. K. Pandey, Spectrvchim.  Acta, Part A, 39, 925 (1983).  10. (a) G. Schmid and G. Ritter, Angew.  Chem.  Int.  Ed. Engl,  (1983). (b) G. Schmid and G.Ritter, Chem. Ber., 103, 3008 (1975). 11. S. 0. G r i m and E. D. Walton, Inorg. Chem., 19, 1982 (1980). 94  14, 645  12. T. S. A . Hor and A . L . C. Tan, Inorg. Chim. Acta , 142, 173 (1988). 13. D. Sallin, Personal Communucation.  95  Chapter 6  GENERAL  6.1  CONCLUSIONS  Conclusions  The analysis of kinetic data for the reaction between P d B r ( d p m ) , l b and 2  2  2  H S is consistent with, and can be accounted for, by either'of mechanisms (a) 2  (Eqs. 3.3 and 3.4) and (b) (Eqs. 3.5 - 3.7). The first order dependence on both P d complex and H S does not distinguish between the two mechanisms. The 2  2  detection of a transient hydride intermediate at low temperatures shows that the reaction proceeds through the oxidative addition of H S across the metal2  metal bond. Further, the rapid decomposition of the hydride intermediate at ambient conditions indicates that the formation of the hydride (or the H S 2  adduct in E q 3.5) is the rate determining step.  Obviously, more extensive  kinetic studies on related systems, especially for complexes of the same metal, are necessary before any conclusion regarding the generality of any mechanism can be reached for H S reactivity toward dimers. 2  Low temperature timr experiments show that the reaction between HBr and l b proceeds stepwise. The oxidative addition of the first mole of HBr results in the formation of a hydride intermediate; this then reacts with the second mole of HBr to form dihydrogen and a tetrabromo complex, P d B r ( d p m ) , 2  4  2  which subsequently fragments slowly to the Pd(II) monomer, PdBr (dpm). 2  The bound ^-sulfide ligand was effectively abstracted from the A-frame  96  complex, Pd X (dpm) (/i-S), by dpm to generate the Pd(I) dimer, Pd X (dpm) , 2  2  2  2  2  along with dpm monosulfide as the only sulfur-containing co-product. It was also demonstrated that the sulfur could be transferred to an organic moiety such as biphenyl. Apart from these systems with stoichiometric sulfur transfer, an effective catalytic system was unearthed. Catalytic desulfurization of H S was effected in the presence of Pd X (dpm) and excess dpm along with 2  2  2  2  the formation of dpmS as the only sulfur-containing product.  6.2  Recommendations for future work  Further studies should be pursued to distinguish between the proposed mechanisms (a) and (b). This could be accomplished by utilizing Pd(I) dpm complexes with different auxiliary ligands (i.e. varying X in Pd X (dpm) ) as well 2  2  2  as other dinuclear complexes of transition metals. So far, there are no kinetic models available for the reactions between H S and dinuclear metal complexes 2  that generate dihydrogen gas. There is little doubt that future investigations in these areas would lead to the improvement of the present system as well as to new systems for the generation of dihydrogen. Understanding the kinetic and the mechanistic aspects of the the reaction that leads to the desulfurization of H S by Pd X (dpm) could lead to the utilization of an economically 2  2  2  2  more viable sulfur acceptor moiety instead of the bisphosphine dpm. Also the synthetic potential of this reaction to transfer sulfur to specific sites should be explored in greater detail.  97  2  

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