eta super(4)-HBCC- sigma , pi -Borataally l Complexes of Ruthenium Comprising an Agostic Interaction

Thermolysis of [Cp*Ru(PPh sub(2)(CH sub(2))PPh sub(2))BH sub(2)(L sub(2))] 1 (Cp*= eta super(5)-C sub(5) Me sub(5); L=C sub(7)H sub(4)NS sub(2)), with terminal alkynes led to the formation of eta super(4)- sigma , pi -borataallyl complexes [Cp*Ru( mu -H)B{R-C=CH sub(2)}(L) sub(2)] (2a-c) and eta super(2)-vinylborane complexes [Cp*Ru(R-C=CH sub(2))BH(L) sub(2) ] (3a-c) (2a, 3a: R=Ph; 2b, 3b: R=COOCH sub(3); 2c, 3c: R=p-CH sub(3)-C sub(6)H sub(4); L=C sub(7)H sub(4)NS sub(2)) through hydroboration reaction. Ruthenium and the HBCC unit of the vinylborane moiety in 2a-c are linked by a unique eta super(4)-interaction. Conversions of 1 into 3a-c proceed through the formation of intermediates 2a-c. Furthermore, in an attempt to expand the library of these novel complexes, chemistry of sigma -borane complex [Cp*RuCO( mu -H)BH sub(2)L] 4 (L=C sub(7)H sub(4)NS sub(2 )) was investigated with both internal and terminal alkynes. Interestingly, under photolytic conditions, 4 reacts with methyl propiolate to generate the eta super(4)- sigma , pi -borataallyl complexes [Cp*Ru( mu -H)BH{R-C=CH sub(2)}(L)] 5 and [Cp*Ru( mu -H)BH{HC=CH-R}(L)] 6 (R=COOCH sub(3); L=C sub(7)H sub(4)NS sub(2)) by Markovnikov and anti-Markovnikov hydroboration. In an extension, photolysis of 4 in the presence of dimethyl acetylenedicarboxylate yielded eta super(4)- sigma , pi -borataallyl complex [Cp*Ru( mu -H)BH{R-C=CH-R}(L)] 7 (R=COOCH sub(3); L=C sub(7)H sub(4)NS sub(2)). An agostic interaction was also found to be present in 2a-c and 5-7, which is rare among the borataallyl complexes. All the new compounds have been characterized in solution by IR, super(1)H, super(11)B, super(13)CNMR spectroscopy, mass spectrometry and the structural types were unequivocally established by crystallographic analysis of 2b, 3a-c and 5-7. DFT calculations were performed to evaluate possible bonding and electronic structures of the new compounds. Building bridges: Hydroboration of sigma -borane complexes with alkynes form novel eta super(4)- sigma , pi -borataallyl complexes (see figure). An agostic interaction was also found to be present, which is rare among the borataallyl complexes.