Novel O , O′ ‐Donor Oxo‐Mo IV Hydrotris(3‐isopropylpyrazolyl)borate Complexes Formed by Chelation of Potentially Hydrogen‐Bonding Phenolate Ligands on Reduction of Dioxo‐Mo VI Complexes

Abstract

The oxo-MoIV complexes formed in the reactions of cis-TpiPrMoVIO2(OAr-R) [TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate, –OAr-R = phenolate derivative] complexes with PEt3 or PEt2Ph in acetonitrile depend on the nature of the potential hydrogen-bonding group (R) incorporated into the phenolate ligand. Green, diamagnetic, oxo(phosphoryl)-MoIV complexes, TpiPrMoIVO(OAr-R)(OPR′3), are produced when R is absent or is a non-coordinating group such as 2-OMe and 3-NEt2; six-coordinate TpiPrMoO(OC6H4OMe-2)(OPEt3) was structurally characterized and exhibits a distorted octahedral geometry typical of such species. When R is a carbonyl functionality, complete oxygen atom transfer leads to green or purple, diamagnetic, chelate complexes of the type, TpiPrMoIVO(OAr-R-κ2O,O′). The R = 2-COEt, 2-CO2Me and 2-CO2Ph derivatives exhibit six-coordinate, distorted-octahedral structures possessing fac TpiPr, terminal oxo and bidentate O,O′-donor –OAr-R ligands. Where R is an amido functionality, CONHPh, the complexes, TpiPrMoIVO(OC6H4CONHPh-2-κ2O,O′)·OPR′3 (R′3 = Et3, Et2Ph), are isolated. Here, the six-coordinate, distorted-octahedral complex forms an intermolecular NH···OPR′3 hydrogen bond to the lattice OPR′3 molecule. Thus, facile chelation of potential hydrogen-bonding phenolate ligands suppresses hydrogen-bond-stabilized aquation or hydroxylation cis to the oxo group in these MoIV complexes.