Bicyclic phosphines as ligands for cobalt catalysed hydroformylation. Crystal structures of [Co(Phoban[3.3.1]-Q)(CO)(3)](2) (Q = C(2)H(5), C(5)H(11), C(3)H(6)NMe(2), C(6)H(11))

A range of tertiary bicyclic phosphine ligands derived from cis, cis-1,5-cyclooctadiene (Phoban family) was studied by batch autoclave reactions during the hydroformylation of a mixture of linear internal decenes using a cobalt catalyst system. Comparative runs were performed with PBu(3) as representative of standard trialkyl phosphine behaviour. The Phoban ligands comprise of a cyclooctyl bicycle with a mixture of the [3.3.1] and [4.2.1] isomers where the third substituent was systematically varied, Phoban-Q (Q = CH(2)CH(3), (CH(2))(4)CH(3), (CH(2))(9)CH(3), (CH(2))(19)CH(3), (CH(2))(3)N(CH(3))(2), C(6)H(11) and C(6)H(5)). An increase in ligand concentration resulted in a decrease in the reaction rate while the selectivity towards the n-alcohol product increased in accordance with a move from more unmodified catalysis to more modified catalysis. Alcohol yields of 77-85% were obtained at rates of 1.8-2.4 h(-1) for highly modified catalysis. Under highly modified conditions the linearity of the alcohol ranges in a narrow band from approximately 85-90% from Phoban-Ph to Phoban-Cy respectively. Hydrogenation of the alkene substrate varied from approximately 9-15% for Phoban-Ph and Phoban-Cy respectively the least and most electron donating derivatives. The two phosphine isomers were separated for Phoban-C(2) and the hydroformylation activity were re-evaluated for each isomer. The less electron donating [4.2.1] isomer required slightly higher ligand concentrations to achieve fully modified catalysis and gave rates and linearities comparable to the [3.3.1] isomer but giving slightly higher yields due to less hydrogenation of the olefin. In comparison, at fully modified conditions, PBu(3) gave a rate of 0.6 h(-1), alcohol yield of 77%, linearity of 81% and 17% hydrogenation. The crystal structures of the cobalt dimers [Co(CO)(3)(Phoban[3.3.1]-C(2))](2), [Co(CO)(3)(Phoban[3.3.1]-C(5))](2), [Co(CO)(3)(Phoban[3.3.1]-C(3)NMe(2))](2), and [Co(CO)(3)(Phoban[3.3.1]-Cy)](2) have been determined and indicated very similar geometries with Co-Co and Co-P bond distances ranging from 2.6526(10)-2.707(3) and 2.1963(8)-2.2074(9) A respectively. The cone angles of the Phoban ligands were calculated from the crystallographic data, according to the Tolman model, and ranges from 159-165 degrees.