Interaction of triosmium complexes with hydrogen chloride: A model for fine-tuning regioselective protonation in metal clusters

The reaction of Os-3(CO)(10)(CNR)(NCMe) (1) with HCl was studied and this s ystem was found to be a good model for observing the fine-tuning of site-se lective protonation in metal complexes. Three products including the proton ated species [(mu-H)Os-3(CO)(10)(CNR)(NCMe)]Cl-+(-) (2), the bridging amino carbyne complex (mu-Cl)Os-3(CO)(10)(mu(2)-C = NHR) (3), and the hydride der ivative (mu-H)Os3Cl(CO)(10)(CNR) (4) were obtained for the reaction. The si te of protonation, either on the Os center or on the nitrogen atom of coord inated isocyanide, was tuned in a sensitive manner by the nature of the coo rdinated isocyanides, the polarity of the solvents, and the strengths of th e acids, leading to different product distributions. The more electron with drawing isocyanides (CNCH2Ph, CNPh) favor the formation of the aminocarbyne complex 3. In a nonpolar solvent like cyclohexane the reaction afforded 3 as the main product. Furthermore, complex 2 was converted to (mu-H)Os-3(CO) (10)(mu(2)-CONHR) (5) upon hydrolysis, in which the coordinated isocyanide was transformed to a carboxamido group. This was verified by obtaining the deuterated species (mu-H) Os-3(CO)(10)(mu(2)-CONDPr) when [(mu-H)Os-3(CO)(1 0)(CNPr)(NCMe)]Cl-+(-) (2a) was treated with D2O in THF. The molecular stru ctures of (mu(2)-Cl)Os-3(CO)(10) (mu(2)-C = NHCH2Ph) (3b) and (mu-H)Os3Cl(C O)(10)(CNPr) (4a) were determined by X-ray diffraction analyses. Complex 3b contains both bridging chloride and bridging aminocarbyne groups, whereas 4a contains a terminal chloride, a terminal isocyanide and a bridging hydri de.