Synthesis of the complexes [N(PPH 3) 2][M(CO) 2(η 3-C 3H 5)-(η 6-7, 9-C 2B 10H 10Me 2)](M = Mo or W): crystal structure of [N(PPH 3) 2][WBr(CO) 3(η 6-7,9-C 2B 10H 10Me 2)

Abstract

Treatment of the compounds [MBr(CO) 2(NCMe) 2(η 3-C 3H 5)] (M = Mo or W) with Na 2[7,9-C 2B 10H 10Me 2] in tetrahydrofuran, followed by addition of [N(PPh 3) 2]Cl, affords the salts [N(PPh 3) 2][M(CO) 2(η 3-C 3H 5)(η 6-7,9-C 2 B 10H 10Me 2)]. Reactions of [N(PPh 3) 2] 2[M(CO) 3(η 6-7,9-C 2B 10H 10Me 2)] with an excess of allyl bromide generate the complexes [N(PPh 3) 2][MBr(CO) 3 (η 6-7,9-C 2B 10H 10Me 2)] via an allyl-coupling process. The structure of the latter (M = W) has been determined by X-ray diffraction. The preparation of the molybdenum salt [N(PPh 3) 2] [MoBr(CO) 3(η 6-7,9-C 2B 10H 10Me 2)] by this route was accompanied by the formation of small amounts of the complex [N(PPh 3) 2][MoBr(CO) 3(η 5-7,9-C 2B 9H 9Me 2)] resulting from ejection of a BH vertex from the cage. Indeed, it was observed that in CH 2Cl 2 solutions, the former species was slowly converted into the latter at ambient temperatures. Protonation (aqueous HBr) of the salts [N(PPh 3) 2][M(CO) 2(η 3-C 3H 5)(η 6-7,9-C 2B 10H 10Me 2)] in the presence of an atmosphere of CO also yields the compounds [N(PPh 3) 2][MBr(CO) 3(η 6-7,9-C 2B 10H 10Me 2)], but if the molybdenum compound is protonated in the absence of CO the complex [N(PPh 3) 2][MoBr(CO) 3(η 5-7,9-C 2B 9H 9Me 2)] is formed directly. The NMR data for the new compounds are reported and discussed, as are the possible pathways of their formation.