Selective reduction of a Pd pincer PCP complex to well-defined Pd(0) species

Abstract

Well-defined dimeric or polymeric Pd(0) complexes [Pd(μ-(iPr)PCHP)](n) (n = 2 or ∞) containing the bridging ligand α,α'-bis(diisopropylphosphino)-m-xylene ((iPr)PCHP) are produced under mild conditions when the cyclometallated PCP pincer complex ((iPr)PCP)Pd-OH reacts with methanol or isopropanol.

β‐Hydrogen Elimination Reactions of Nickel and Palladium Methoxides Stabilised by PCP Pincer Ligands

“…As anticipated from our previous studies on the decomposition of the palladium hydroxide [( i Pr PCP)Pd‐OH],7 authentic samples of [( i Pr PCP)Pd‐OMe] exhibit the same behaviour as the hydroxide when heated in methanol, and decay into the [Pd(μ‐ i Pr PCHP)] 2 dimer (Scheme ). 31 P{ 1 H} NMR spectroscopic monitoring of this transformation reveals the gradual appearance of the characteristic low‐frequency signal of the dimeric Pd 0 product ( δ =42.9 ppm), until its concentration reaches a certain threshold above which it precipitates quantitatively.…”

“…Thermal decomposition of Ni and Pd methoxide complexes As anticipated from our previous studies on the decomposition of the palladium hydroxide [( iPr PCP)Pd-OH], [7] authentic samples of [( iPr PCP)Pd-OMe] exhibit the same behaviour as the hydroxide when heated in methanol, and decay into the [Pd(m-iPr PCHP)] 2 dimer (Scheme 1). 31 P{ 1 H} NMRs pectroscopicm onitoring of this transformation reveals the graduala ppearance of the characteristic low-frequency signal of the dimeric Pd 0 product (d = 42.9 ppm), until its concentration reaches ac ertain threshold above which it precipitates quantitatively.B eyond this point, the resonance of the Pd 0 product disappears from the spectrum but the intensity of the startingm ethoxide (d = 59.4 ppm) continues to decrease with respect to that of O= PPh 3 added as an internal standard.…”

“…This strain is released by its conversion into the corresponding Pd 0 dimer, [Pd(μ‐PCHP)] 2 , as observed experimentally. We previously calculated that this process is thermodynamically favourable by approximately 14 kcal mol −1 7…”

“…Complexes [( i Pr PCP)M‐OMe] and [( i Pr PCP)M‐H] (M=Ni, Pd) were prepared as described previously 6c. 7 NMR spectra were recorded by using a Bruker DRX 400 MHz spectrometer. Chemical shifts ( δ ) are reported in ppm.…”

“…[6] We recently reported that the palladium hydroxide complex [( iPr PCP)Pd-OH]i sr eadily reduced by methanol or isopropanol to aw ell-defined Pd 0 species through as equence of reactions that involve the decomposition of the intermediate methoxide or isopropoxide complexes [( iPr PCP)Pd-OR] (R = Me, iPr) by bhydrogen elimination (BHE). [7] This reactivity pattern could be involved in many catalytic reactions in which pincerc omplexes act as precursors for reduced species or metal nanoparticles, which are the true active catalysts. [8] However,B HE also plays an essential role in reactions that are actively catalysed by pincer complexes,s uch as alcohol dehydrogenation, oxidation or coupling with imines or amines.…”