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Ruthenium diphosphine complexes with auxiliary nitrogen-donor ligands

University of British Columbia

A group of ruthenium(II) complexes possessing chelating diphosphine ligands (P-P) was prepared, and their reactivity was studied. The diphosphines employed were DPPB (l,4-bis(diphenylphosphino)butane), (R)-BINAP (P)-2,2'- bis(diphenylphosphino)-l,l'-binaphthyl), and (S,S)-DIOP ((S,S)-2,3-0-isopropylidene- 2,3-dihydroxy-l,4-bis(diphenylphosphino)butane), which form seven-membered chelate rings. [chemical formulas not included] Most work involved the characterization and chemistry of Ru(II)(P-P) complexes containing ancillary N-donor ligands. The complexes are readily prepared from RuCl₂(P-P)(PPh₃) (P-P = DPPB or (R)-BINAP) and heterocyclic, pyridyl-based ligands (monodentate L, and bidentate L₂). With the monodentate L ligands, the trans-RuCl₂ ((R)-BINAP)(L)₂ complexes are formed, while for the bidentate L₂ ligands, isomerization of trans- to cis-RuCl₂ ((R)-BINAP)(L₂) occurs, via both photochemical and thermal processes. Cis-RuX₂ ((R)-BINAP)(L₂) (X = Br, I; L₂ = bipy, phen) were prepared by halide metathesis from the corresponding dichloro species. Restricted rotation of the pyridyl rings in the trans-RuCl₂ ((R)-BINAP)(L)₂ species, and of the phenyl rings in all the trans- RuCl₂ ((R)-BINAP)(L)₂ and cis-RuX₂((R)-BINAP)(L₂) complexes, was detected by variable temperature NMR spectroscopy. X-ray crystallographic determinations of the structures of trans-RuCl₂ ((R)-BINAP)(py)₂, cis-RuCl₂ ((R)-BINAP))(phen), cis- RuCl₂ ((R)-BINAP))(bpa), and cis-RuBr₂ ((R)-BINAP))(bipy) show the presence of arene-stacking interactions involving the binaphthyl backbone of BINAP, as well as phenyl and pyridyl rings. The arene-stacking is proposed to result in the restricted rotations observed spectroscopically in solution. Unusual temperature- and solvent-dependent ³¹P{¹H} NMR spectroscopic behaviour was observed for most of the cis-RuX₂((R)-BlNAP)(L₂) complexes, in which unexpected degeneracy of the two ³¹P signals occurs at specific solvent and temperature combinations which differ for each complex. Reaction of the RuCl₂ (P-P)(L₂) complexes with H₂ in the presence of base gives Ru(H)Cl(P-P)(L₂) species, while reaction with CO gives [RuCl(CO)(P-P)(L₂)]Cl, these species being characterized in situ by NMR spectroscopy. Cationic, solvento complexes of type [RuCl(P-P)(L₂)(RCN)]PF₆ (where R = Me, Ph) and [Ru(P-P)(L₂)(H₂O)(OTf)]OTf (OTf= CF₃SO₃⁻) were prepared from RuCl₂ (P-P)(L₂), and characterized, including structural determinations of cis-[RuCl(DPPB)(bipy)(MeCN)]PF₆ and cis- [Ru(DPPB)(phen)(H₂O)(OTf)]OTf. Several of the complexes mentioned above were tested for catalytic activity in the homogeneous hydrogenation of the aldimines PhC(H)=NCH₂Ph and PhC(H)=NPh, and preliminary results are presented. The aerial oxidation of one P-atom of the diphosphine in RuCl₂ (P-P)(L₂) was discovered serendipitously, and synthetic routes to bis(phosphine) monooxide (BPMO) complexes from cis-RuCl₂ (P-P)(L₂) species were subsequently developed. RuCl₂ (DPPBO)(L₂) and [RuCl(BINAPO)(L₂)]PF₆ complexes were prepared (where DPPBO = l-(diphenylphosphinoyl)-4-(diphenylphospino)butane; BINAPO = (R)-2- (diphenylphosphinoyl)-2'-(diphenylphosphino)-l,l'-binaphthyl), and a novel tridentate coordination mode of BINAPO via the P¹¹¹- and O-atoms, as well as η²-naphthyl coordination (see below), was characterized by X-ray crystallography. [chemical formulas not included] Reaction of RuCl₂((R)-BINAP)(PPh₃) with CO in solution yields trans- RuCl₂ (BINAP)(CO) ₂, which isomerizes to the cis form in the absence of excess CO. In the solid state, RuCl₂ ((R)-BINAP)(PPh₃) reacts rapidly with CO to form trans-RuCl₂ ((R)- BINAP)(PPh₃)(CO), which isomerizes to the cis form in the solid state and in solution. Preparation of RuCl₂ ((R)-BINAP)(CO)₂ is also possible by a solid state reaction. The reactions of RuCl₂ ((R)-BINAP)(PPh₃) with monodentate S-donor ligands (L = DMSO (dimethylsulfoxide), TMSO (tetramethylenesulfoxide), DMS (dimethylsulfide)) gave the diruthenium Ru₂Cl₄(BINAP)₂ (L) species. The reactions of RuCl₂ (P-P)(PPh₃) (P-P = DPPB, (R)-BINAP) with the disulfoxide BESE (meso-l,2-bis(ethylsulfinyl)ethane) gave cis-RuCl₂ (P-P)(BESE), and the DPPB complex was structurally characterized and shown to possess S-bonded disulfoxide. The reactions of RuCl₂ (P-P)(PPh₃) (P-P = DPPB, (R)-BINAP) with the dialkylammonium salts [H₂NR₂]Cl (R = ethyl, n-butyl) gave the ionic [H₂NR₂][Ru₂Cl₅(PP)₂] species. Oxidation of the mixed-valence Ru₂Cl₅(P-P)₂ (P-P = DPPB, (S,S-DIOP) by Cl₂ gave Ru(III) species isolated as RuCl₃(P-P)(H₂O), and RuCl₃(P-P)(DMSO) complexes were prepared by reaction of DMSO with the aqua species.

Thesis/Dissertation

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2009-09-18

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http://hdl.handle.net/2429/12899

Chemistry

University of British Columbia

UBCV

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