Our group has reported that addition of acetophenone or nitrobenzene to precursors of (PCP)Ir (PCP = k3-2,6-C6H3(CH2PtBu2)) yields six-coordinate iridium(III) trans-C-H complexes (PCP)IrH(k2-O,C-acetophenyl) and (PCP)IrH(k2-O,C-nitrophenyl) respectively; the geometry indicates that C-H addition precedes rather than being followed by, coordination of the carbonyl or nitro oxygen. These complexes are converted to the cis-C-H isomers upon heating at 130 �C for ca. 5 hours.1 We have found that the same pattern is observed with PCOP- and POCOP-type pincer ligands. In contrast, C-H addition of 2-phenylpyridine gives trans-C-H isomers which do not isomerize even after 300 hours at 130 �C. We have begun to investigate a newly developed phosphino-amino NCOP pincer ligand (k3-[1,3-C6H3(OPR2)(CH2NR2)]). (NCOP)IrHCl reacts with 2-phenylpyridine in presence of NaOtBu to yield the trans-C-H complex (NCOP)IrH(k2-N,C-(2-phenylpyridinyl)); this isomerizes to the cis-C-H species much more readily than the PCP/PCOP/POCOP complexes, but still requires several weeks at room temperature. Surprisingly, we find that addition of a large excess of alkene (tert-butylethylene or vinyltrimethylsilane) promotes the trans/cis isomerization such that it occurs in 1 hour at room temperature; the cis-C-H product is obtained in apparent equilibrium with another product apparently resulting from alkene coordination. Moreover, catalytic amounts of pyridine (10 mol%) were found to effect a clean trans/cis isomerization process in 10 h at room temperature with no co-products observed. Our hypothesis at this point is based on the presumed hemilability of the NCOP ligand; replacement of the amino group by an alkene or pyridine ligand gives an intermediate capable of undergoing isomerization followed by recoordination of the amino group. This may well be relevant to our recent observation that the (NCOP)Ir complex (also in contrast its PCP-type analogs) catalyzes the addition of the pyridylphenyl ortho-C-H bond across olefinic double bonds.1. Goldman, A. S. et al J. Am. Chem. Soc. 2004  , 126, 13192.

Catalyzed cis/trans isomerization of Ir-H(k<sup>2</sup>-N,C-(2-phenylpyridinyl)) complexes supported by a hemilabile phosphino-amino NCOP pincer ligand and promoted by pyridine and alkenes at room temperature

246th National Meeting (2013)

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Catalyzed cis/trans isomerization of Ir-H(k2-N,C-(2-phenylpyridinyl)) complexes supported by a hemilabile phosphino-amino NCOP pincer ligand and promoted by pyridine and alkenes at room temperature

Catalyzed cis/trans isomerization of Ir-H(k²-N,C-(2-phenylpyridinyl)) complexes supported by a hemilabile phosphino-amino NCOP pincer ligand and promoted by pyridine and alkenes at room temperature