Theoretical investigation of the binding of small molecules and the intramolecular agostic interaction at tungsten centers with carbonyl and phosphine ligands.

The factors controlling both the binding of small molecules to several tungsten complexes and agostic bonding in the W(CO)3(PCy3)2 complex have been examined through B3LYP hybrid density functional theory and ab initio MP2 calculations with and without basis set superposition error (BSSE) corrections. This approach attempts to isolate insofar as possible the separate effects of intrinsic bonding interactions, electron induction by ligands, and steric hindrance and strain. An important conclusion from this study is that for bimolecular reactions, BSSE corrections must be included for quantitative predictions.

Dihydrogen complexes as prototypes for the coordination chemistry of saturated molecules.

The binding of a dihydrogen molecule (H(2)) to a transition metal center in an organometallic complex was a major discovery because it changed the way chemists think about the reactivity of molecules with chemically "inert" strong bonds such as H H and C H. Before the seminal finding of side-on bonded H(2) in W(CO)(3)(PR(3))(2)(H(2)), it was generally believed that H(2) could not bind to another atom in stable fashion and would split into two separate H atoms to form a metal dihydride before undergoing chemical reaction. Metal-bound saturated molecules such as H(2), silanes, and alkanes (sigma-complexes) have a chemistry of their own, with surprisingly varied structures, bonding, and dynamics.

Synthesis, structure, and thermochemistry of the formation of the metal-metal bonded dimers [Mo(mu-TeAr)(CO)3(PiP3)]2 (Ar = phenyl, naphthyl) by phosphine elimination from *Mo(TePh)(CO)3(PiPr3)2.

The complexes (*TeAr)Mo(CO)3(PiPr3)2 (Ar = phenyl, naphthyl; iPr = isopropyl) slowly eliminate PiPr3 at room temperature in a toluene solution to quantitatively form the dinuclear complexes [Mo(mu-TeAr)(CO)3(PiPr3)]2. The crystal structure of [Mo(mu-Te-naphthyl)(CO)3(PiPr3)]2 is reported and has a Mo-Mo distance of 3.2130 A.

Comparison of thermodynamic and kinetic aspects of oxidative addition of PhE-EPh (E = S, Se, Te) to Mo(CO)3(PR3)2, W(CO)3(PR3)2, and Mo(N[tBu]Ar)3 complexes. The role of oxidation state and ancillary ligands in metal complex induced chalcogenyl radical generation.

Enthalpies of oxidative addition of PhE-EPh (E = S, Se, Te) to the M(0) complexes M(PiPr3)2(CO)3 (M = Mo, W) to form stable complexes M(*EPh)(PiPr3)2(CO)3 are reported and compared to analogous data for addition to the Mo(III) complexes Mo(N[tBu]Ar)3 (Ar = 3,5-C6H3Me2) to form diamagnetic Mo(IV) phenyl chalcogenide complexes Mo(N[tBu]Ar)3(EPh). Reactions are increasingly exothermic based on metal complex, Mo(PiPr3)2(CO)3 < W(PiPr3)2(CO)3 < Mo(N[tBu]Ar)3, and in terms of chalcogenide, PhTe-TePh < PhSe-SePh < PhS-SPh. These data are used to calculate LnM-EPh bond strengths, which are used to estimate the energetics of production of a free *EPh radical when a dichalcogenide interacts with a specific metal complex.

High-spin diimine complexes of iron(II) reject binding of carbon monoxide: theoretical analysis of thermodynamic factors inhibiting or favoring spin-crossover.

A new series of Fe(II) complexes, FeCl2[N(R)=C(Me)C(Me)=N(R)], containing diimine ligands with hemilabile sidearms R (R = CH2(CH2)2NMe2, 1, CH2(CH2)2OMe, 2, CH2(CH2)2SMe), 3) were synthesized. The crystal structure of 1 showed 6-coordination where both amine arms were attached, whereas 2 was a 5-coordinate 16e species with one methoxy arm dangling free. Extensive attempts were made to bind CO to these species to synthesize precursors for dihydrogen complexes but were unsuccessful.

C-H Activation and C-C coupling of arenes by cationic Pt(II) complexes.

The synthesis and characterization of cationic platinum complexes of the type [(R(2)PC(2)H(4)PR(2))PtMe(OEt(2))]BAr(F) (R = Cy, Et) are reported. These electrophilic platinum cations are found to react quantitatively with arenes (benzene, toluene) at room temperature by undergoing intermolecular C-H activation with concomitant C-C coupling to generate complexes of the type [[Pt(R(2)PC(2)H(4)PR(2))](2)(mu-eta(3):eta(3)-biaryl)][BAr(F)](2). The dianionic biaryl ligands in these compounds exhibit a rare mu-eta(3):eta(3)-bis-allyl bonding mode and can be removed from the complex with stoichiometric oxidants to generate the free biaryl and [(R(2)PC(2)H(4)PR(2))Pt(mu-X)](2)[BAr(F)](2) (R = Cy, Et; X = Cl, I).

Reversible Displacement of Polyagostic Interactions in 16e [Mn(CO)(R(2)PC(2)H(4)PR(2))(2)](+) by H(2), N(2), and SO(2). Binding and Activation of eta(2)-H(2) trans to CO Is Nearly Invariant to Changes in Charge and cis Ligands.

Electrophilic 16e [Mn(CO)(R(2)PC(2)H(4)PR(2))(2)](+) complexes (R = Et, Ph) are synthesized by metathesis of MnBr(CO)(R(2)PC(2)H(4)PR(2))(2) with Na or Li salts of low-coordinating boron or gallium anions (e.g., [B{C(6)H(3)(3,5-CF(3))(2)}(4)](-) or [Ga(C(6)F(5))(4)] (-)).

Comparison of H-H versus Si-H sigma-Bond Coordination and Activation on 16e Metal Fragments. Organosilane, N(2), and Ethylene Addition to the Agostic Complex W(CO)(3)(PR(3))(2) and Dynamic NMR Behavior of the Latter.

Variable-temperature (31)P{(1)H} NMR spectroscopy of the agostic complexes M(CO)(3)(PCy(3))(2) (M = Mo, W) indicates dynamic behavior as evidenced by collapse below -20 degrees C of a singlet to an AB signal plus a shifted singlet. The inequivalency of the phosphines is possibly due to the presence of conformational isomers resulting from hindered rotation of the M-P bond or, less likely, a geometric isomer with pseudo-cis PCy(3) ligands. Further studies on the coordination chemistry of W(CO)(3)(PR(3))(2) (R = iPr, Cy) were performed.