Synthesis of trans-[Mo(O)(F)(dppe)(2)](BF(4)), trans-[Mo(O)(OH)(dppe)(2)](ClO(4)), and trans-[Mo(O)(2)(dppe)(2)].2L (L = H(2)O, CH(3)OH, CH(3)CH(2)OH, CH(3)CHOHCH(3)). Crystal Structure of trans-[Mo(O)(2)(dppe)(2)].2CH(3)OH

Oxygen Atom Transfer Reactivity from a Dioxo-Mo(VI) Complex to Tertiary Phosphines: Synthesis, Characterization, and Structure of Phosphoryl Intermediate Complexes

The oxygen atom transfer (OAT) reactivity of TpMoO2Cl with PMe3, PEt3, and PPhMe2 (where Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate) has been investigated. The OAT reactions proceed through a diamagnetic Mo(IV) phosphoryl intermediate complex of general formula TpMoOCl(OPR3) (OPR3 = OPMe3, OPEt3, OPPhMe2), which have been isolated and characterized by 1H and 31P NMR, UV-visible, and infrared spectroscopies and electrospray ionization mass spectrometry. Solid-state crystal structures of TpMoOCl(OPMe3) and TpMoOCl(OPPhMe2) are also reported, the oxygen-to-phosphorus distances agree with a double-bond formulation and a single bond between the metal and the phosphoryl oxygen atom. The stability of the phosphoryl intermediate complexes depends on the steric properties of the coordinated phosphine-oxides. These intermediate complexes have been converted to solvent-coordinated species, TpMoOCl(solv) (solv = acetonitrile or dmf), and the coordinated solvents exchange with the bulk solvent.

Rhenium oxo complexes of a chelating diyne ligand. Synthesis and study of the kinetics of protonation

A series of oxo complexes, Re(O)X(diyne) (X = I, Me, Et), have been prepared from 2,7-nonadiyne and Re(O)I(3)(PPh(3))(2). Addition of B(C(6)F(5))(3) to Re(O)I(2,7-nonadiyne) (5) results in coordination of the oxo ligand to the boron. The protonation of Re(O)(X)(2-butyne)(2) and Re(O)(X)(2,7-nonadiyne)(2) with a variety of acids has been examined. With 5 and HBF(4)/Et(2)O, the ultimate product was [Re(CH(3)CN)(3)(I)(2,7-nonadiyne)](2+) (7). The conversion of 5 to 7 changes the conformation of the diyne ligand from a "chair" to a "boat" and shifts its propargylic protons considerably downfield in the (1)H NMR. The kinetics of the protonation of Re(O)I(2,7-nonadiyne) (5) by CF(3)SO(3)H in CH(3)CN have been monitored by visible spectroscopy, in a stopped-flow apparatus, and by low temperature (1)H NMR. Two second-order rate constants, presumably successive protonations, were observed in the stopped-flow, k(1) = 11.9 M(-)(1) s(-)(1) and k(2) = 3.8 M(-)(1) s(-)(1). Low temperature (1)H NMR spectroscopy indicated that the resulting solution contained a mixture of two doubly protonated intermediates X and Y, each of which slowly formed the product 7 via an acid-independent process.

Synthesis and Characterization of a Stable trans-Dioxo Tungsten(IV) Complex and Series of Mono-Oxo Molybdenum(IV) and Tungsten(IV) Complexes. Structural and Electronic Effects of pi-Bonding in trans-[M(O)(X)(dppe)(2)](+/0) Systems

trans-[W(O)(F)(dppe)(2)](BF(4)) (dppe = Ph(2)PCH(2)CH(2)PPh(2), 1,2-bis(diphenylphosphino)ethane) (10) has been synthesized. From this, the neutral trans-[W(O)(2)(dppe)(2)].2CH(3)OH (11) was prepared by a hydrolysis and deprotonation reaction with Et(4)NOH in methanol/water. Together with the analogous molybdenum compound (2) this compound afforded by substitution under acid conditions salts of trans-[M(O)(X)(dppe)(2)](+) ions (M = Mo, W; X = OH, OCH(3), Cl, Br, I, NCS) and trans-[Mo(O)(N(3))(dppe)(2)](CF(3)SO(3)) (9). All the compounds have low-spin d(2) electronic configuration. The compounds were characterized by (31)P{(1)H} NMR, positive FAB-ionization mass spectrometry, UV-vis spectroscopy, and vibrational spectroscopy. X-ray crystallographic studies were carried out on compounds 10, 11, trans-[W(O)(OH)(dppe)(2)](ClO(4)) (12), and trans-[W(O)(NCS)(dppe)(2)](BPh(4)) (16). The electronic spectra of the mono-oxo species are consistent with the lowest energy transitions being of d(xy)() --> {d(zx)(), d(yz)()} character. No ligand-field transitions are observed for the dioxo tungsten complex. Identical pi-spectrochemical series were found for the two metals. The shielding of the phosphorus nuclei determined by (31)P{(1)H} NMR is significantly influenced by the nature of the axial ligands.