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Aryl and amido nitrosyl complexes of molybdenum and tungsten Ross, Kevin J.


Treatment of CpW(NO)(o-tolyl)₂ with water affords CpW(O)(N-o-tolyl)(o-tolyl) and CpW(O) 2(o-tolyl) in the ratio 1: 1. Labeling studies indicate that the conversion of CpW(NO)(o-tolyl)₂ to CpW(O)(N-o-tolyl)(o-tolyl) is an intramolecular isomerization. The solid-state molecular structures of CpW(NO)(o-tolyl)₂ and CpW(O)(N-o-tolyl)(o tolyl) were determined by single-crystal X-ray studies. Various analogues of CpW(NO)(o-tolyl)₂ do not undergo isomerization upon treatment with water. At present, the conversion of CpW(NO)(o-tolyl)₂ to CpW(O)(N-o-tolyl)(o-tolyl) mediated by water is a unique chemical transformation. Nitrosyl N-O bond cleavage is also observed upon thermolysis of the complex Cp*W(NO)Ph₂. From this thermolysis, the complexes Cp*W(n²ONPh)(NPh)(Ph), [Cp *w(o)phf.p..N1Cp *W(1.40)Ph] and Cp*W(O) ₂Ph are isolated in low to moderate yields. Thermolysis of Cp*W(NO)Ar 2(Ar = Ph, p-tolyl) in the presence ofPhSSPh produces Cp*W(NO)(Ar)(SPh) in high yields. The bulk of this work involves the synthesis and study of a variety of amido containing complexes. Complexes of the type Cp’M(NO)(H₂NHR)Cl₂ ,Cp’M(NO)(NHR)Cl Cp’M(NO)(R)(NHR), Cp’M(NO)(OR)(NHR) and CpM(NO)(NHR)₂ have been synthesized and characterized. The effect of the various ligands on the JR spectroscopic and electrochemical properties of some of the complexes are also presented. Two representative complexes, Cp*Mo(NO)(H₂NPh)Cl₂ and Cp*W(NO)(OCMe 3)(NHCMe₃) have been subjected to single-crystal X-ray analyses. The reactivity of two representative amido chioro complexes, Cp*W(NO)(NHp tolyl)Cl and Cp*W(NO)(NHCMe₃)Cl, was investigated. Reaction of the alkylamido chloro complex with heterocumulenes affords mono-insertion products, while treatment with t-butyl isocyanide produces (Me₃CNC)₄ W(NO)Cl. Exposure ofCH₂Cl ₂solutions of Cp*W(NO)(NHCMe₃)Clto the atmosphere results in the formation of [Me₃CNH₃]₃[Cp*W(O)₃]₂Cl,which was characterized by an X-ray crystallographic analysis. Treatment of the complexes Cp*M(NO)(NHptolyl)Cl with LDA affords complexes of the type [Cp*M(NO)NHAr]-µNAr[Cp*M(NO)ClJ, Ar p-tolyl. A VT NMR study of the molybdenum complex revealed an activation barrier of 13(1) kcal/mol (5 3(4) kJ/mol) for rotation about the N-C bond of the bridging imido group. Complexes of the type C)3p(*WO(NOT)(XCMe₃)(OTf) (X = NH or 0) were also synthesized. Three complexes, namely Cp*W(NO)(CH₂CMe₃)(NHCMe₃), Cp*W(NO)(OCMe₃), differ only in the nature of a pair of groups a to the metal center. The reactivities of these complexes toward p-tolyl isocyanate, carbon disulfide and t-butyl isoëyanide were studied. The results of these reactions indicate that the tungsten-nitrogen and -oxygen linkages react preferentially over the tungsten-carbon linkage for reactions with heterocumulenes. In contrast, the tungsten-carbon linkage is the preferential site of reactivity for t-butyl isocyanide. These results can be rationalized by invoking two mechanisms in these systems: one which involves nucleophilic attack by the bound ligand or, alternatively, adduct formation followed by migration/insertion to afford the formal insertion products. Kinetic evidence suggests that the reaction between Cp*W(NO)(OCMe₃)(NHCMe₃) and p-tolyl isocyanate is a simple bimolecular reaction. The insertion complex, Cp*W(NO)(ɳ²-C{NCMe₃)(CH₂CMe₃)(OCMe₃) was studied by X-ray analysis. This study confirms that the site of insertion is the tungsten-carbon bond and that the resulting iminoacyl ligand is bound in an ɳ² fashion. The reactivity of the three complexes Cp*W(NO)(XCMe₃)₂ (X = NH, 0 and CH₂) was also studied. In the case of Cp*W(NO)(CH₂CMe₃)₂ a competing reaction is the dominant process. This process is proposed to involve the expulsion of neopentane to form the transient complex Cp*W(NO)(=CHCMe₃) which activates C₆D₆ to form Cp*W(NO)(CHDCMe₃)(C₆D₅).

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