Coordination chemistry of late transition metals with PCP ligands. Synthesis, catalysis and mechanism

Sammanfattning: Abstract The work presented in this thesis discusses synthesis of PCP-complexes and utilisations of such organometallic compounds in catalysis. The complexes, obtained by intramolecular Csp3-H activation, are based on the metals palladium, platinum and iridium. The synthesis of PCP-ligands include new and improved preparative routes to the previously known cis-1,3-bis-(di-iso-propylphosphinito)cyclohexane (6), cis-1,3-bis[(di-tert-butylphosphino)cyclohexane (1) and the new compound cis-1,3-Bis-(di-tert-butylphosphinito)cyclohexane (5). With dichloro(1,5-cyclooctadiene)platinum(II) the phosphinite ligands were reluctant to Csp3-H activate and gave cis-[PtCl2{cis-1,3-bis-(di-iso-propylphosphinito)}-cyclohexane] (7) along with the di-nuclear trans-[PtCl2{cis-1,3-Bis-(di-tert-butyl-phosphinito)-cyclohexane}]2 complex. The platinum precursor successfully produced the PCsp3P-complex cis-[2,6-bis(di-tert-butylphosphinomethyl)cyclohexyl-?3P,C1,P?]-chloroplatinum(II) (8) with the phosphine ligand 1. With the dinuclear precursor bis(1,5-cyclooctadiene)diiridium(I) dichloride the phosphine ligand 1 gave the Csp3-H activated hydrido complex cis-[2,6-bis(di-tert-butylphosphinomethyl)cyclohexyl-?3P,C1,P?]chlorhydridoiridium(III) (9).Substitution on the previously known cis-[2,6-bis(di-tert-butylphosphinomethyl)cyclohexyl-?3P,C1,P?]trifluoroacetopalladium(II) (2) produced cis-[2,6-bis(di-tert-butylphosphinomethyl)cyclohexyl-?3P,C1,P?]bromide-palladium(II) (10) and cis-[2,6-bis(di-tert-butylphosphinomethyl)cyclohexyl-?3P,C1,P?]phenylpalladium(II) (11) with NaBr and PhLi, respectively. The catalytic properties of the aromatic PCP complex {2,6-bis[(diphenyl-phosphino)methyl]-benzene}-(trifluoroacetato)palladium(II) was investigated in the Stille reaction and proved to be an excellent catalyst for the C?C cross-coupling between trimethyl phenyl stannane and aryl bromides using a very low catalyst loading at elevated temperature. Mercury poisoning test and a kinetic investigation of the catalytic reaction suggests a colloidal palladium catalyst formed from the PCP Pd(II) pre-catalyst. The aliphatic complex 2 was investigated as a precatalyst for the Suzuki reaction of aryl halides with phenylboronic acid in the absence or presence of mercury to give the product in modest to reasonably good yields. Stepwise reactions, monitored by 31P- and 1H-NMR spectroscopy concluded that complex 2 preferred activated boronic acid over aryl halide in the first reaction step to yield the phenyl complex 11. The phenyl complex thereafter generated the corresponding bromo complex 10 and the Suzuki cross coupling product upon addition of aryl halide. The investigation proves that palladium PCP complexes can mediate cross-coupling reactions in an elevated oxidation state.