Heterobimetallic Activation of Dioxygen:  Characterization and Reactivity of Novel Cu(I)−Ge(II) Complexes

Abstract

Reaction of the known germylene Ge[N(SiMe 3 ) 2 ] 2 and a new heterocyclic variant Ge [(NMes) 2 (CH) 2 ] with [L Me2 Cu] 2 (L Me2 = the β -diketiminate derived from 2-(2,6-dimethylphenyl) amino-4-(2,6-dimethylphenyl)imino-2-pentene) yielded novel Cu(I)-Ge(II) complexes L Me2 Cu-Ge [(NMes) 2 (CH) 2 ] (1a) and L Me2 Cu-Ge[N(SiMe 3 ) 2 ] 2 (1b), which were characterized by spectroscopy and X-ray crystallography. The lability of the Cu(I)-Ge(II) bond in 1a and b was probed by studies of their reactivity with benzil, PPh 3 , and an N-heterocyclic carbene (NHC). Notably, both complexes are cleaved rapidly by PPh 3 and the NHC to yield stable Cu(I) adducts (characterized by X-ray diffraction) and the free germylene. In addition, the complexes are highly reactive with O 2 and exhibit chemistry which depends on the bound germylene. Thus, oxygenation of 1a results in scission and formation of thermally unstable L Me2 CuO 2 , which subsequently decays to [(L Me2 Cu) 2 (μ-O) 2 ], while 1b yields L Me2 Cu(μ-O) 2 Ge[N(SiMe 3 ) 2 ] 2 , a novel heterobimetallic intermediate having [Cu III (μ-O) 2 Ge IV ] 3+ core. The isolation of the latter species by direct oxygenation of a Cu(I)-Ge(II) precursor represents a new route to heterobimetallic oxidants comprising copper.Efforts to understand the mechanisms of oxidation catalysis 1 are aided by studies aimed at isolating and characterizing metal-oxygen intermediates in proteins 2 and synthetic systems. 3 Such intermediates are often derived from reactions of reduced metal sites with the versatile and abundant reagent O 2 , and particular attention has been placed on those species that incorporate a single type of metal ion. For instance, extensive examination of the reactions of O 2 with Cu(I) complexes has led to the identification of a variety of binding motifs and activation pathways of relevance to important biological processes. 4 Mixed metal systems that operate synergistically to activate O 2 also are of interest, as they are implicated in some synthetically and biologically useful catalytic reactions. Notable examples that involve Cu include Cu-Pd species in Wacker-type oxidations 5 and Cu-Fe intermediates in cytochrome c oxidase. 3d,6Examples of well-characterized heterobimetallic oxygen intermediates derived from O 2 are rare, however, due in part to the challenges associated with preventing formation of products arising from oxygenation of only one of the two types of metal ions provided in the starting material(s). Nonetheless, mixed heme-Fe/nonheme-Cu species with peroxo and oxo bridges have been isolated from reactions of Fe(II)-Cu(I) precursors. 6 In addition, heterobimetallic bis (μ-oxo)CuNi or -CuPd species have been generated by reacting isolable 1:1 Cu/O 2 species 7 or (PPh 3 ) 2 PdO 2 with a mononuclear complex of a reduced metal (e.g. Ni(I) or Cu(I), respectively). 8 While this "stepwise" approach toward the synthesis of heterobimetallic oxygen intermediates is attractive, we were intrigued by the reported 9 discoveries that the two metal ions in (PR...

Transition Metal Complexes of N‐Heterocyclic Germylenes

“…The benzo-anellated bis(NHGe)-Mo(CO) 4 chelate complex 4 [23] behaves similarly to 2b, with displacements for Ge of 13.5 pm and for Mo of 65 pm, whereas in a sterically even more challenging but non-anellated (dimesityl-NHGe)Cu I complex there are no marked deviations from planarity (Ge: 0.8 pm; Cu: 2.8 pm). [31] To shed light on the background of the folding observed for the anellated NHGe carbonyl molybdenum(0) and nickel(0) complexes (Figure 3), we calculated the structure of 2a in the gas phase, along with the structures of [Ge{(NtBu) 2 . Compound 2a is planar in the solid state [15c] with both neopentyl groups on the same side, but the 0.22 kcal mol -1 required to achieve planarity can easily be provided by packing effects.…”

Theoretical Exploration of the Oxidative Properties of a [(trenMe1)CuO2]+ Adduct Relevant to Copper Monooxygenase Enzymes: Insights into Competitive Dehydrogenation versus Hydroxylation Reaction Pathways

“…Keywords: copper · density functional calculations · dioxygen · enzyme models · hydroxylation · oxidation Whereas coupled dinuclear copper systems have been the subject of a large number of theoretical and experimental studies, [28][29][30] investigations of the oxidative processes induced by mononuclear copper-O 2 adducts are less common. The main reason is that model compounds usually undergo fast dimerization or exhibit slow reactivity.…”

The role of the bis-trimethylsilylamido ligand, [N{SiMe3}2]−, in main group chemistry. Part 2: Structural chemistry of the metallic p-block elements

“…The novel Cu(I)-Ge(II) containing compound Cu(BDI Ar ) [Ge(N{SiMe 3 } 2 ) 2 ] (Ar = 2,6-Me 2 C 6 H 3 , 87) was reported in 2006, in which the copper centre was supported by a bidentate BDI-ligand [78]. It was shown that this bond can be readily cleaved by donor ligands such as PPh 3 or an NHC with liberation of the free germylene, whereas reaction with O 2 insterted into the Cu Ge bond to afford the Cu(II)-Ge(IV) species, Cu(BDI Ar )( -O) 2 [Ge(N{SiMe 3 } 2 ) 2 ] (88, Eq.…”