Exchange of boryl ligand substituents in Os[B(OEt)2]Cl(CO)(PPh3)2

Reaction between Os[B(OEt)2]Cl(CO)(PPh3)2 and 1,2-ethanediol in the presence of Me3SiCl (1 equivalent) leads to the tethered boryl complex, Cl(CO)(PPh3)2 (1), in which one ethoxy substituent on the boryl ligand is exchanged with one hydroxy group of the 1,2-ethanediol leaving the other OH group available to coordinate to osmium, so giving a six coordinate complex. This formulation is confirmed by crystal structure determination. The same reactants, but with 2 equivalents of Me3SiCl, lead to the yellow, coordinatively unsaturated complex, OsCl(CO)(PPh3)2 (2). Complex (2) adds CO to give OsCl(CO)2 (PPh3)2 (3). Crystal structure determinations of 2 and 3 reveal a very marked difference in the Os–B distances found in the five coordinate complex 2 (2.043(4) Å) and the six coordinate complex 3 (2.179(7) Å). In a reaction similar to that used for forming 2 but with 1,3-propanediol replacing 1,2-ethanediol, the product is OsCl(CO)(PPh3)2 (4). The crystal structure for 4 is also reported.