Stepwise Expansion of Pd Chains from Binuclear Palladium(I) Complexes Supported by Tetraphosphine Ligands
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- 作者：Tomoaki Tanase ; Satoko Hatada ; Sayo Noda ; Hiroe Takenaka ; Kanako Nakamae ; Bunsho Kure ; Takayuki Nakajima
- 刊名：Inorganic Chemistry
- 出版年：2015
- 出版时间：September 8, 2015
- 年：2015
- 卷：54
- 期：17
- 页码：8298-8309
- 全文大小：621K
- ISSN：1520-510X
文摘
Reaction of [Pd2(XylNC)6]X2 (X = PF6, BF4) with a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), afforded binuclear PdI complexes, [Pd2(渭-dpmppm)2]X2 ([2]X2), through an asymmetric dipalladium complex, [Pd2(渭-dpmppm)(XylNC)3]2+ ([1]2+). Complex [2]2+ readily reacted with [Pd0(dba)2] (2 equiv) and an excess of isocyanide, RNC (R = 2,6-xylyl (Xyl), tert-butyl (tBu)), to generate an equilibrium mixture of [Pd4(渭-dpmppm)2(RNC)2]2+ ([3鈥瞉2+) + RNC 鈬?[Pd4(渭-dpmppm)2(RNC)3]2+ ([3]2+), from which [Pd4(渭-dpmppm)2(XylNC)3]2+ ([3a]2+) and [Pd4(渭-dpmppm)2(tBuNC)2]2+ ([3b鈥瞉2+) were isolated. Variable-temperature UV鈥搗is and 31P{1H} and 1H NMR spectroscopic studies on the equilibrium mixtures demonstrated that the tetrapalladium complexes are quite fluxional in the solution state: the symmetric Pd4 complex [3b鈥瞉2+ predominantly existed at higher temperatures (>0 掳C), and the equilibrium shifted to the asymmetric Pd4 complex [3b]2+ at a low temperature (鈭尖垝30 掳C). The binding constants were determined by UV鈥搗is titration at 20 掳C and revealed that XylNC is of higher affinity to the Pd4 core than tBuNC. In addition, both isocyanides exhibited higher affinity to the electron deficient [Pd4(渭-dpmppmF2)2(RNC)2]2+ ([3F鈥瞉2+) than to [Pd4(渭-dpmppm)2(RNC)2]2+ ([3鈥瞉2+) (dpmppmF2 = meso-bis[{di(3,5-difluorophenyl)phosphinomethyl}phenylphosphino]methane). When [2]X2 was treated with [Pd0(dba)2] (2 equiv) in the absence of RNC in acetonitrile, linearly ordered octapalladium chains, [Pd8(渭-dpmppm)4(CH3CN)2]X4 ([4]X4: X = PF6, BF4), were generated through a coupling of two {Pd4(渭-dpmppm)2}2+ fragments. Complex [2]2+ was also proven to be a good precursor for Pd2M2 mixed-metal complexes, yielding [Pd2Cl(Cp*MCl) (Cp*MCl2)(渭-dpmppm)2]2+ (M = Rh ([5]2+), Ir ([6]2+), and [Au2Pd2Cl2(dpmppm鈥揌)2]2+ ([7]2+) by treatment with [Cp*MCl2]2 and [AuCl(PPh3)], respectively. Complex [7]2+ contains an unprecedented PC(sp3)P pincer ligand with a PCPCPCP backbone, dpmppm鈥揌 of deprotonated dpmppm. The present results demonstrated that the binuclear PdI complex [2]2+ was a quite useful starting material to extend the palladium chains and to construct Pd-involved heteromultinuclear systems.
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