The activation of tertiary amines by osmium cluster complexes: Further studies of the reaction of Os3(CO)10(NCMe)2 with triethylamine

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Abstract
The reactions of Os3(CO)12 and Os3(CO)10(NCMe)2 with NEt3 have been reinvestigated. Two new products, Os3(CO)10(μ‐CH2C(H)NEt2)(μ‐H)) (2) and Os3(CO)10(syn‐μ‐η1‐CHCHNEt2)(μ‐H) (3) were obtained in low yields, 4% and 7%, in addition to the previously reported compound Os3(CO)10(anti‐μ‐η1‐CHCHNEt2(μ‐H) (1) (20% yield) when the reaction was conducted at 25°C using Os3(CO)10(NCMe)2. Compounds 2 and 3 were characterized by IR, 1H NMR and single‐crystal X‐ray diffraction analyses. Compound 2 contains a bridging methyl‐metallated N‐ethylimine ligand formed by the cleavage of one ethyl group from the NEt3. Compound 3 is an isomer of 1 in which the bridging ligand has a syn conformation with respect to the cluster as compared with the anti conformation in 1. Compound 3 slowly isomerizes to 1. Compound 3 is de‐carbonylated by exposure to UV radiation and is transformed to the new compound Os3(CO)9(μ3‐CC(H)NEt2)(μ‐H)2 (4) (58% yield) by an additional CH activation to form a triply bridging η1‐diethylaminovinylidene ligand. Compound 4 isomerizes to the compound Os3(CO)9(μ3‐HCCNEt2)(μ‐H)2 (5) (70% yield) at 68°C. The latter contains a triply briding ynamine ligand which exhibits structural and reactivity features that are characteristic of a carbene ligand at the amine‐substituted carbon atom. Crystal data: for 2, space group = P21/c, a = 9.236(2) Å, b = 12.469(2) Å, c = 18.107(3) Å, β = 104.67(1)°, Z = 4, 2518 reflections, R = 0.031; for 3, space group = P21/m, a = 7.644(1) Å, b = 12.706(2) Å, c = 11.912(2) Å, β = 108.02(1)°, Z = 2, 1295 reflections, R = 0.030; for 4, space group = P21/n, a = 10.233(2) Å, b = 14.834(4) Å, c = 14.538(2) Å, β = 99.88(2)°, Z = 4, 2403 reflections, R = 0.036.

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