Synthesis, characterisation and catalytic investigation of a new type of PC(sp3)P pincer Pd(II) complex

The diphosphine cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane (2) has been synthesised and its complexation in palladium chemistry has been investigated. Ligand 2 is capable of tricoordination, for instance as demonstrated by an X-ray crystal structure determination of the complex [Pd(2)I], and it is a rare example of a PC(sp(3))P pincer ligand. A catalytic study of the Heck reaction revealed that the bis-chelated complex [Pd(2)(CO2CF3)] is a highly active, air-stable precatalyst in the olefination of iodo- and bromo-benzenes. It is evident that, in comparison with the analogous aromatic PC(sp(2))P system, by switching the hybridisation of the central carbon donor atom from sp(2) to sp(3) improvement in terms of catalytic activity is achieved.