Reversible displacement of polyagostic interactions in 16e [Mn(CO)(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2}]{sup +} by H{sub 2}, N{sub 2}, and SO{sub 2}. Binding and activation of {eta}{sup 2}-H{sub 2} trans to CO is nearly invariant to changes in charge and cis ligands
- Los Alamos National Lab., NM (United States)
Electrophilic 16e [Mn(CO)(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2}]{sup +} complexes (R = Et, Ph) are synthesized by metathesis of MnBr-(CO)(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2} with Na or Li salts of low-coordinating boron or gallium anions (e.g., [B{l_brace}C{sub 6}H{sub 3}(3,5-CF{sub 3}){sub 2}{r_brace}{sub 4}]{sup {minus}} or [Ga(C{sub 6}F{sub 5}){sub 4}]{sup {minus}}). They contain weal polyagostic interactions that are reversibly displaced by H{sub 2}, N{sub 2}, and SO{sub 2} (which is a surprisingly weak ligand here). The agostic and H{sub 2} complexes, as well as the gallium anions including the new species [{l_brace}Ga(C{sub 6}F{sub 5}){sub 3}{r_brace}{sub 2}({mu}-Cl)]{sup {minus}}, have been characterized by NMR, IR, and X-ray crystallography. The agostic Mn-H distances (e.g., 2.9 {angstrom}) are much longer than those found for the single agostic interactions in Mo(CO)(diphosphine){sub 2} and [Mn(CO){sub 3}(PCy{sub 3}){sub 2}]{sup +}. The H-H and also the Mn-H distances have been determined in the H{sub 2} complex by T{sub 1} measurements for both the H{sub 2} and HD isotopomers. IR data and C-O and M-C bond lengths are used to gauge the {pi}-acceptor strengths of ligands trans to the CO. The agostic C-H bonds are the weakest ligands and also the weakest acceptors, but the H{sub 2} ligand is an excellent acceptor as strong as N{sub 2} and ethylene. The variation of {nu}(CO) on increasing the basicity of the cis-phosphine (dppe versus depe) in trans-M(CO)(diphosphine){sub 2}(L) is less than expected and far less than that on increasing the charge on the complex (M = Mn{sup +} versus Mo). The H-H bond lengths (0.87--0.90 {angstrom}) and J(HD) NMR couplings (32--34 Hz) in [Mn(CO)(R{sub 2}PC{sub 2}H{sub 4}Pr{sub 2}){sub 2}(H{sub 2})]{sup +} and other cationic H{sub 2} complexes with trans-CO are strikingly similar to their neutral analogues and nearly invariant. Activation of H-H in the more electrophilic cationic systems occurs primarily via increased {sigma} donation from H{sub 2} as compared to the more electron-rich neutral analogues where back-bonding dominates. The nature of the ligand trans to H{sub 2} (the strong acceptor CO here) controls the H-H distance more so than all of the cis ligands combined, especially for cationic complexes.
- OSTI ID:
- 346929
- Journal Information:
- Inorganic Chemistry, Vol. 38, Issue 6; Other Information: PBD: 22 Mar 1999
- Country of Publication:
- United States
- Language:
- English
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