INSERTION OF ETHYNE INTO THE RU-B BOND OF A COORDINATIVELY UNSATURATED RUTHENIUM BORYL COMPLEX - X-RAY CRYSTAL-STRUCTURE OF RU(CH=CH[BOC6H4O])CL(CO)(PPH3)(2)

Ethyne inserts readily into the Ru-B bond of the five-coordinate boryl complex Ru-(BO2C6H4)Cl(CO)(PPh3)(2) (1) to form the borylalkenyl comp lex Ru(CH=CH[BOC6H4O])Cl(CO)(PPh3)(2) (2). Complex 2 has been characte rized by IR and multinuclear NMR spectroscopy and by an X-ray crystal structure determination. In the solid state, the Ru atom in 2 is six c oordinate through weak attachment of a catechol oxygen to ruthenium. T wo further products, Ru(CH=CHB[OCH2CH2O])Cl(CO)(PPh3)(2) (3) and Ru(CH =CHB[OEt][OEt])Cl(CO)(PPh3)(2) (4), which result from transesterificat ion of 2 with HOCH2CH2OH and 3 with CH3CH2OH, respectively, are also d escribed. The relevance of the observed ethyne insertion for metal-cat alyzed hydroboration is discussed.