Development of Structurally Constrained Metal Clusters Leading to Functional Nano-Molecular Devices

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Linear transition-metal clusters have recently attracted increasing attention concerning their unique structural, optical, and electrochemical properties. Attempts to build up much expanded molecules with multi-functional metal-metal interactions are highly desired in relation to development of molecular-based electronic devices as well as to exploration of unprecedented physical and chemical behaviors. In this project, we have studied the syntheses, characterization, and reactivities of linear hexanuclear clusters. Reduction of Pt_3 complex 1 with NaBH_4 in E_tOH afforded the linear hexaplatinum cluster, [Pt_6(μ-H)(μ-dpmp)_4(RNC)_2(PF_6)_3 (3), whereas the analogous heterometallic cluster, [Pt_4Pd_2(μ-H)(μ-dpmp)_4(RNC)_2](PF_6)_3 (4), was synthesized from reaction of Pt_2Pd complex 2 with NaOMe ([PL_2M(μ-dpmp)_2(RNC)_2](PF_6)_2 (M=Pt (1), Pd (2); dpmp=bis(diphenyl- phosphinomethyl)phenylphosphine, RNC=organoisocyanide). Complex 3a (R=Xyl) is a trivalent, 86e-cluster and involves a linear Pt_6 core (Pt-Pt(central)=3.3092(5) Å, Pt-Pt(inner)=av. 2.733 Å, Pt-Pt(outer)= av. 2.704 Å) supported by four dpmp ligands and terminally coordinated by two isonitriles. The clusters 3a and 4a readily underwent two-electron oxidation to afford [Pt_4Pd_2(μ-dpmp)_4(RNC)_2](PP_6)_4 (M=Pt (5a), Pd (5b)). Reduction of 1 with NaBH_4 in DMF afforded dark green trihydride hexaplatinum complex, [Pt_6(μ-H)(H)_2(μ-dpmp)_4](PF_6) which was interestingly converted into neutral hexplatinum cluster with coordinatively unsaturated terminals, [Pt_6(μ-H)_2(μ-dpmp)_4] (6). The trihydride cluster readily reacted with Mel to give [Pt_6(μ-H)(I)_2(μ-dpmp)_4](PF_6). These linear clusters with hydrides could be of significant importance as reactive functional metal wires coupled with redox processes. The SAM's (self assembled monolayer) of bisisocyanide-linked 3a were prepared and characterized by electrochemical methods.