5-Diphenylphosphino-2-hydroxy-1,3-xylyl-18-crown-5 has been synthesized from 5-bromo-2-hydroxy-18-crown-5 by reacting it in sequence at low temperature with n-butyl lithium and methyl diphenylphosphonite. The phosphorous donor properties of this phenol phosphine (OH derivative) and the corresponding phenoxide (O- derivative) have been studied in the presence and absence of alkali metal ions by determining the frequencies of the A(1) nu(CO) bands of Ni(CO)(3)L complexes. For the OH and O- derivatives, the latter generated by addition of CsOH to the former, the nu(CO) bands are observed at 2067.6 and 2063.4 cm(-1), respectively, providing the trend predicted by Hammett parameters for OH and O- substituents. Addition of Na+ or K+ to the OH derivative has little effect on this stretching frequency, but the former ion shifts the O- derivative band to 2067.7 cm(-1). A solid state structure has been obtained of the OH derivative, and two independent molecules were found in the unit cell. Both have a single water molecule hydrogen bonded to two across-ring oxygen atoms and the phenol hydrogen. The crown ether ring has the usual gauche and anti arrangements for the C-C and C-O bonds.

A series of niobium and tantalum aryloxide complexes containing pyridylethyl ligation have been synthesized via 2-vinylpyridine insertion to metal hydride complexes.

We describe herein the novel application of a transition metal oxo complex, a cationic oxorhenium(V) oxazoline, in the production of molecular hydrogen (H2) from the catalytic hydrolytic oxidation of organosilanes. The main highlights of the reaction are quantitative hydrogen yields, low catalyst loading, ambient conditions, high selectivity for silanols, water as the only co-reagent, and no solvent requirement. The amount of hydrogen produced is proportional to the water stoichiometry. Thus, reaction mixtures of polysilyl organics such as HC(SiH3)3 and water contain potentially >6 wt % hydrogen. Kinetic and isotope labeling experiments have revealed a new mechanistic paradigm for the activation of Si-H bonds by oxometalates.

The rhenium oxo complex [Re(O)(hoz)2][TFPB], 1 (where hoz = 2-(2'-hydroxyphenyl)-2-oxazoline(-) and TFPB = tetrakis(pentafluorophenyl)borate) catalyzes the hydrosilation of aldehydes and ketones under ambient temperature and atmosphere. The major organic product is the protected alcohol as silyl ether. Isolated yields range from 86 to 57%. The reaction requires low catalyst loading (0.1 mol %) and proceeds smoothly in CH2Cl2 as well as neat without solvent. In the latter condition, the catalyst precipitates at the end of reaction, allowing easy separation and catalyst recycling. Re(O)(hoz)(H), 3, was prepared, and its involvement in an ionic hydrosilation mechanism was evaluated. Complex 3 was found to be less hydridic than Et3SiH, refuting its participation in catalysis. A viable mechanism that is consistent with experimental findings, rate measurements, and kinetic isotope effects (Et3SiH/Et3SiD = 1.3 and benzaldehyde-H/benzaldehyde-D = 1.0) is proposed. Organosilane is activated via eta2-coordination to rhenium, and the organic carbonyl adds across the coordinated Si-H bond [2 + 2] to afford the organic reduction product.