American Chemical Society
om300760j_si_004.cif (16.33 kB)

Monomeric Rhodium(II) Complexes Supported by a Diarylamido/Bis(phosphine) PNP Pincer Ligand and Their Reactivity Toward Dihydrogen

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posted on 2013-04-08, 00:00 authored by Dan A. Smith, David E. Herbert, Justin R. Walensky, Oleg V. Ozerov
A rhodium­(II) complex of a diarylamido/bis­(phosphine) PNP pincer ligand, (PNP)­Rh­(OTf) (2, where OTf = O3SCF3 and PNP = [κ3-P,N,P-(4-Me-2-(iPr2P)-C6H3)2N]), has been prepared by oxidation of the rhodium­(I) precursor (PNP)­Rh­(H2CCHBut) (1) with AgOTf. A series of related rhodium­(II) complexes of the general formula (PNP)­Rh­(X) (where X = OAc (3), OSiPh3 (4), OC6H4F (5), Cl (6)) was synthesized via simple anion metathesis reactions starting from 2. In addition, complexes 3 and 6 could be prepared by hydrogen atom abstraction from (PNP)­Rh­(H)­(OAc) (7) or (PNP)­Rh­(H)­(Cl) (8) with TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)­oxyl). Solid-state X-ray structures of compounds 26 revealed an approximately square-planar environment about Rh. Analysis of the structural features of 26, EPR spectroscopic data, and DFT computational studies are most consistent with a +2 oxidation state for rhodium. Reactions of 2, 3, 5, and 6 with H2 were explored. The reaction of 2 with H2 gave the new complex (PN­(H)­P)­Rh­(H)2(OTf) (9), and the reaction of 3 with H2 produced (PNP)­Rh­(H)­(OAc) (7), whereas the reaction of 5 with H2 gave the known (PNP)­Rh­(H2) (10), all with complete consumption of the starting rhodium­(II) complexes. In contrast, the reaction of 6 with H2 produced a mixture of (PNP)­Rh­(H)­(Cl) (8) and (PN­(H)­P)­Rh­(H)2(Cl) (11) in apparent equilibrium with 6 and H2. (PNP)­Rh­(H2) (10) was identified as an elongated dihydrogen complex.