CLUSTERS CONTAINING CARBENE LIGANDS .7. PREPARATION OF OS3(CO)8[C(H)NME2](MU-3-S)(MU-H)2 AND THE NATURE OF ITS REACTIONS WITH SECONDARY AND TERTIARY-AMINES

Os3(CO)9(μ3-CO)(μ3-S) and Os3(CO)10(μ-SPh)(μ-H) were found to react with NMe3 to yield the complex Os3-(CO)8[C(H)NMe2](μ3-S)(μ-H)2 (1a) in yields of 31% and 26%, respectively. Os3(CO)10(μ-CNMe2)(μ-H) was found to react with H2S to yield 1a in 36% yield. Compound 1a was analyzed by a single-crystal X-ray diffraction analysis and was found to contain a secondary (dimethylamino)carbene ligand terminally coordinated to a sulfur-bridged triosmium cluster. The amino group in the carbene ligand was exchanged by reactions of 1a with NEt2H and NPr2 nH at 56 and 80 °C and by reaction with NEt3 or NPr3n at 145 °C in MeOH solvent. Significant amounts of [Os3(CO)9(μ3-S)(μ-H)]- (3) are also formed in the latter reactions. The diamine HN(Et)(CH2)2NMe2 reacted with 1a at 80 °C to give Os3(CO)8[C(H)N(Et)(CH2)2NMe2](μ3-S)(μ-H)2 (1e) in 42% yield, le was decarbonylated at 145 °C to give Os3(CO)7[C(H)N(Et)(CH2)2NMe2](μ3-S)(μ-H)2 (2e) in 41% yield. Compound 2e was characterized by a single-crystal X-ray diffraction analysis and was found to contain a terminally coordinated C(H)N(Et)(CH2)2NMe2 carbene ligand chelated to the cluster through coordination of the NMe2 group. Labeling studies have shown that the reactions of the carbene complexes with tertiary amines involve C-H activation processes in the alkyl groups and exchange of the amino group of the carbene ligand. A mechanism is proposed that involves iminium ligand intermediates that couple to the carbene ligand to form a nitrogen-containing metallacycle. Solutions of 1a in methanol were found to catalyze the exchange of alkyl groups between NEt3 and NPr3n, but analyses of the catalyst mixtures have shown that most of the catalysis was produced by 3, a decomposition product of the carbene-containing cluster complexes. Crystal data: (for 1a) space group P1, a = 8.703 (1) Å, b = 12.226 (2) Å, c = 18.980 (4) Å, α = 85.30 (1)° β = 78.65 (1)°, γ= 72.29 (1)°, R = 0.043 for 3554 reflections; (for 2e) space group P21/n, a = 11.774 (3) Å, b = 12.712(2) Å, c = 14.712 (4) Å, β = 104.82 (2)°, R = 0.050 for 1866 reflections. © 1990, American Chemical Society. All rights reserved.