Studies Relevant to the Functional Model of Mo-Cu CODH: In Situ Reactions of Cu(I)-L Complexes with Mo(VI) and Synthesis of Stable Structurally Characterized Heterotetranuclear MoVI2CuI2 Complex

Abstract

In this study, we report the synthesis, characterization, and reactions of Cu(I) complexes of the general form Cu(L)(LigH2) (LigH2 = xanthene-based heterodinucleating ligand (E)-3-(((5-(bis(pyridin-2-ylmethyl)amino)-2,7-di-tert-butyl-9,9-dimethyl-9H-xanthen-4-yl)imino)methyl)benzene-1,2-diol); L = PMe3, PPh3, CN(2,6-Me2C6H3)). New complexes [Cu(PMe3)(LigH2)] and [CuCN(2,6-Me2C6H3)(LigH2)] were synthesized by treating [Cu(LigH2)](PF6) with trimethylphosphine and 2,6-dimethylphenyl isocyanide, respectively. These complexes were characterized by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry (HRMS), and X-ray crystallography. In contrast, attempted reactions of [Cu(LigH2)](PF6) with cyanide or styrene failed to produce isolable crystalline products. Next, the reactivity of these and previously synthesized Cu(I) phosphine and isocyanide complexes with molybdate was interrogated. IR (for isocyanide) and 31P NMR (for PPh3/PMe3) spectroscopy demonstrates the lack of oxidation reactivity. We also describe herein the first example of a structurally characterized multinuclear complex combining both Mo(VI) and Cu(I) metal ions within the same system. The heterobimetallic tetranuclear complex [Cu2Mo2O4(μ2-O)(Lig)2]·HOSiPh3 was obtained by the reaction of the silylated Mo(VI) precursor (Et4N)(MoO3(OSiPh3)) with LigH2, followed by the addition of [Cu(NCMe)4](PF6). This complex was characterized by NMR spectroscopy, high-resolution mass spectrometry, and X-ray crystallography.

Combining [MoVIO3] and [M0(CO)3] (M = Mo, Cr) Fragments within the Same Complex: Synthesis and Reactivity of the Single Oxo-Bridged Heterobimetallics Supported by Xanthene-Based Heterodinucleating Ligands

“…Replacement of the iminopyridine chelate by the more robust dipicolylamine (L 2 , Scheme 1) enabled formation of a metastable bimetallic Mo(VI)/Cu(I) species directly observable by NMR spectroscopy and high-resolution mass spectroscopy (HRMS); 28 the related tetrametallic [Mo 2 Cu 2 ] complex was recently structurally characterized. 29 However, no oxidation of the coordinated CNR (isocyanide, a close CO analogue) was observed by the heterobimetallic complex [Cu I Mo VI O 3 (L 2 )] − , 29 and only fleeting CO coordination was observed with the corresponding Cu(I) complex [Cu I (L 2 H 2 )] + . 28 As a possible solution to this problem, we decided to replace it with a π-basic metal known to coordinate the CO strongly.…”

“…Our laboratories have undertaken a different approach toward the design of a functional model of Mo–Cu CODH. – This approach relies on the utilization of a heterodinucleating xanthene-bridged ligand that brings two metals together in addition to/or in the absence of the direct sulfido or oxo bridges. While not fully replicating the active site composition of Mo–Cu CODH, it combines Mo(VI)-oxo (the oxidant) in the vicinity of Cu(I) (the CO “anchor”), thus allowing us to test various hypotheses regarding the structure–activity relationship.…”