Stepwise Expansion of Pd Chains from Binuclear Palladium(I) Complexes Supported by Tetraphosphine Ligands

作者：Tanase Tomoaki; Hatada Satoko; Noda Sayo; Takenaka Hiroe; Nakamae Kanako; Kure Bunsho; Nakajima Takayuki

来源：Inorganic Chemistry, 2015, 54(17): 8298-8309.

DOI：10.1021/acs.inorgchem.5b00950

Reaction of [Pd-2(XyINC)(6)]X-2 (X = PF6, BF4) with a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), afforded binuclear Pd-I complexes, [Pd-2(mu-dpmppm)(2)]X-2 ([2]X-2), through an asymmetric dipallachum complex, [Pd-2(mu-dpmppm)(XylNC)(3)](2+) ([1](2+)). Complex [2](2+) readily reacted with [Pd-0(dba)(2)] (2 equiv) and an excess of isocyanide, RNC (R = 2,6-xylyl (Xyl), tert-butyl (Bu-t), to generate an equilibrium mixture of [Pd-4(mu-dpmppm),(RNC)(2)](2+) ([3'](2+)) + RNC reversible arrow [Pd-4(mu-dpmppm)(2) (RNC)(3)](2+) ([3](2+)), from which [Pd-4(mu-dpmppm)2(XylNC)(3)](2+) ([3a](2+)) and [Pd-4(mu-dpmppm)(2) ((BUNC)-B-t)(2)](2+) ([3b'](2+)) were isolated. Variable-temperature UV-vis and P-31{H-1} and H-1 NMR spectroscopic studies on the equilibrium mixtures demonstrated that the tetrapalladium complexes are quite fluxional in the solution state: the symmetric Pd-4 complex [3b'](2+) predominantly existed at higher temperatures (>0 degrees C), and the equilibrium shifted to the asymmetric Pd-4 complex [3b'](2+) at a low temperature (similar to-30 degrees C). The binding constants were determined by UV-vis titration at 20 degrees C and revealed that XylNC is of higher affinity to the Pd-4 core than (BuNC)-Bu-t. In addition, both isocyanides exhibited higher affinity to the electron deficient [Pd-4(mu-dpmppmF(2))(2)(RNC)(2)](2+) ([3F'](2+)) than to [Pd-4(mu-dpmppm)(2)(RNC)(2)](2+) ([3'](2+)) (dpmppmF(2) = meso-bisadi(3,5-difluorophenyl)phosphinomethyl}phenylphosphino]methane). When [2] X-2 was treated with [Pd-0(dba)(2)] (2 equiv) in the absence of RNC in acetonitrile, linearly ordered octapalladium chains, [Pd-8(mu-dpmppm)(4)(CH3CN)(2)]X-4 ([4]X-4: X = PF6, BF4), were generated through a coupling of two {Pd-4(mu-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)(mu-dpmppm)(2)](2+) (M = Rh ([5](2+)), Ir ([6](2+)), and [Au2Pd2Cl2(dpmppm-H)(2)](2+) ([7])(2+) by treatment with [Cp*MCl2](2) and [AuCl(PPh3)], respectively. Complex [7]2+ contains an unprecedented PC(sp(3))P pincer ligand with a PCPCPCP backbone, dpmppm H of deprotonated dpmppm. The present results demonstrated that the binuclear Pd-I complex [2](2+) was a quite useful starting material to extend the palladium chains and to construct Pd-involved heteromultinuclear systems.

• 出版日期2015-9-7