The reaction of [Mn2{µ-σ:η2-C(R)CHR}(µ-PPh2)(CO)7](R = H or Ph) with nucleophiles: X-ray crystal structures of [N(PPh3)2][Mn2(µ-H){µ-C(O)C(Ph)CHPh}(µ-PPh2)(CO)6], [Mn2{PPh2C(Ph)CHPh}(CO)9], [Mn2(µ-PPh2CHCH2)(CO)8], [Mn2{µ-C(O)C(Ph)CHPh}(µ-PPh2)(CO)6(CNBut)2], [Mn2{µ-σ:η2-C(Ph)CHPh}(µ-PPh2)(CO)6(CNBut)], and [Mn(µ-PPh2CHCH2)(CO)7(PEt3)]

Abstract

The reaction of [Mn₂{µ-σ:η²-C(R)CHR}(µ-PPh₂)(CO)₇](R = H or Ph) with the nucleophiles H^–, CO, Bu^tNC, and PEt₃ have been studied and the structures of six of the products of these reactions have been determined by X-ray diffraction. In all of the products the nucleophile is bound to the metal but the course of a given reaction is highly sensitive both to the nature of the nucleophile and to the substituents on the µ-vinyl group. With H^– as the nucleophile and R = Ph the principal product is the µ-acyl complex [N(PPh₃)₂][Mn₂(µ-H){µ-C(O)C(Ph)CHPh}(µ-PPh₂)(CO)₆] in which the Mn–Mn distance of 2.813(1)Å indicates the presence of a metal–metal bond. With CO as the nucleophile a P–C coupling reaction between the µ-PPh₂ and the µ-vinyl ligand is induced (R = H or Ph) leading via[Mn₂{µ-PPh₂C(R)CHR}(CO)₈] to the final product [Mn₂{PPh₂C(R)CHR}(CO)₉] which results from the addition of a second molecule of the nucleophile. The structures of both of these P–C linked complexes have been determined by X-ray diffraction, the former for R = H and the latter for R = Ph. The Mn–Mn separations for these two complexes are 2.957(1) and 2.941(1)Å, respectively. With Bu^tNC as the nucleophile and R = Ph a µ-acyl complex, [Mn₂{µ-C(O)C(Ph)CHPh}(µ-PPh₂)(CO)₆(CNBu^t)₂], is also obtained as the principal product but the X-ray diffraction study reveals an Mn–Mn separation of 3.820(2)Å indicating the absence of a metal–metal interaction. A second product obtained in this reaction has been shown by an X-ray diffraction study to be the Bu^tNC-substituted vinyl derivative [Mn₂{µ-σ:η²-C(Ph)CHPh}(µ-PPh₂)(CO)₆(CNBu^t)] in which the Mn–Mn distance is 2.758(1)Å. With phosphines as the nucleophiles, complex mixtures of products are, in general, obtained and these products have not all been characterised. With PEt₃ and R = H, however, the principal product is the P–C linked complex [Mn₂(µ-PPh₂CHCH₂)(CO)₇(PEt₃)] and this has been isolated and structurally characterised by an X-ray diffraction study which shows that the Mn–Mn distance is 2.989(3)Å. Finally, with Bu^tNC as the nucleophile and R = H a compound is formed which is tentatively assigned a structure analogous to that obtained with PEt₃ as the nucleophile. Some reaction pathways which account for the formation of the major products in the above reactions are proposed and discussed.