Substitution and insertion reactions of the dinuclear manganese µ-hydride complex [M2(µ-H)(µ-PPh2)(CO)8]; crystal structures of the complexes [Mn2(µ-σ:η2-CHCH2)(µ-PPh2)(CO)7] and [Mn2(µ-H)(µ-PPh2)(CO)6(CNBut)2]

Abstract

[Mn₂(µ-H)(µ-PPh₂)(CO)₈](1) has been synthesised in 80% yield from [Mn₂(CO)₁₀] and PHPh₂. Reaction of (1) with RCN, RNC, PPh₃, P(OMe)₃, or (EtO)₂POP(OEt)₂ gives substitution products of general formulae [Mn₂(µ-H)(µ-PPh₂)(CO)₇L][L = NCMe (2a); NCPh (2b); CNBu^t(2c); CNCH₂Ph (2d); PPh₃(2e); P(OMe)₃(2f); P(OEt)₃(2g)], [Mn₂(µ-H)(µ-PPh₂)(CO)₆L₂][L = CNBu^t(3a); L₂=(EtO)₂POP(OEt)₂(3b)], and [Mn₂(µ-H)(µ-PPh₂)(CO)₄{(EtO)₂POP(OEt)₂}₂](4). Reaction of (1) with alkynes gives the complexes [Mn₂(µ-σ:η²-CRCHR′)(µ-PPh₂)(CO)₇][R = R′= H (5a); R = Ph, R′= H (5b); R = H, R′= Ph (5c); R = R′= Ph (5d); R = R′= CF₃(5e)] which are derived from (1) by insertion of the alkyne into a Mn–H bond together with loss of a CO group. Complexes (3a) and (5a) have been characterised by X-ray structure analysis by conventional heavy-atom methods using room-temperature diffractometer data. Crystals of (3a) are triclinic, space group P, with a= 17.686(3), b= 10.063(2), c= 9.231(3)Å, α= 96.92(4), β= 99.40(4), γ= 104.34(5)°, and Z= 2. 3 047 Reflections with I 3σ(I)[3 ⩽θ⩽ 25°] refined to R= 0.044 and R′= 0.043. The complex (5a) crystallises in space group P with a= 10.301(4), b= 10.320(4), c= 24.359(11)Å, α= 92.70(3), β= 92.17(3), γ= 123.59(3)°, and Z= 4. The structure was solved by a combination of direct methods and Fourier-difference techniques and refined by blocked-cascade least squares to R= 0.047 for 6 036 diffractometer data. Structures are proposed for the other new complexes and the mechanism of formation of the complexes (5) from (1) is discussed.