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-CH=CH₂)(μ-PPh ₂)(CO)₇] and [Mn₂(μ-H)(μ-PPh₂)(CO)₆(CNBu ^t)₂]

[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-CR=CHR′) (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 P1, 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 P1 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.