Synthesis, characterization and reactivity of Group 6 alkoxo nitrosyl complexes

Three new classes of alkoxo nitrosyl complexes of the type Cp*M(NO)(OR)X (Cp* =C5Me5; M = Mo, W; R = alkyl, aryl; X = CI, OR, alkyl), all of which have been fully characterized, are prepared by metathesis reactions. The molecular structures ofCp*W(NO)(OCMe3)2 and Cp*W(NO)(OCH2Ph)2 have been established by X-ray crystallographic analyses. While in general the above metathesis reactions are straightforward, two interesting bimetallic complexes, [Cp*W(N0)(CH2SiMe3)][Cp*W(C1)(0)]-(112-il:T12-NC(H)SiMe3) and [Cp*W(N0)(CH2SiMe3)C1][Cp*W(C1)(i2-N{0){H)CH2SiMe3)]-(1.t-N), are produced in attempts to prepare alkoxo alkyl complexes using potassium salts. X-ray crystallographic analyses of both products are presented. The reaction chemistry of the three classes of alkoxo complexes, Cp*M(NO)(OR)X, with a variety of reagents such as oxygen, water, phosphines, carbon monoxide, dihydrogen, HCI, isonitriles and isocyanates has been investigated. In general, the 18-electron bis(alkoxo)complexes are chemically inert to most of these reagents; the only exceptions being the reactions of Cp*M(NO)(OR)2 with H2 and HC1. The inertness of the bis(alkoxo) complexes is attributed to donation of electron density from filled p-type orbitals on the oxygen atoms into empty metal orbitals on the metal center. The reactivity studies of the chloro compounds are limited because of their extreme air- and moisture-sensitivity. In contrast, the alkoxo alkyl complexes decompose cleanly to isolable organometallic species when treated with 02 or H2O. In Lewis acid-base type reactions with PMe3, CNCMe3, PhNCO and p-tolylNCO, the Cp*M(N0)(R)(OR') species have sufficiently electron-deficient metal centers to form 1:1 adducts and/or insertion products. The diamagnetic bimetallic complex, [Cp*Mo(N0)(CH2Ph)(11-0)]2, is produced when Cp*Mo(NO)(CH2Ph)(OCMe3) is treated with H2 in THF. Earlier work into the reactions of dialkyl complexes, Cp'W(NO)R2 (Cp' = r15-05H5, is-C5Me5), with carbon monoxide has been extended to permit some general conclusions regarding CO-insertion reactions in these systems. These studies show that the products obtained from the carbonylation of various Cp'W(NO)R2 complexes are very dependent upon the nature of the ancillary ligands. The nature of the cyclopentadienyl ligand determines the extent of the reactivity, with only the Cp complexes inserting a second equivalent of CO. The nature of the hydrocarbyl group influences the rate of the reaction such that the greater Lewis acidity of the diaryl complexes results in their forming monoacyl products faster than do the related dialkyl complexes. However, only the monoacyl alkyl complexes possess a sufficiently weak M-C bond to undergo a second insertion of CO to form bis(acyl) species, Cp'W(NO)(C{O}R)2. The nature of the hydrocarbyl ligand also plays an influential role in the case when R = CH2Ar in that putative reductive elimination of ketone occurs from the undetectable monoacyl intermediate complexes.Science, Faculty ofChemistry, Department ofGraduat