Comparative binding of H{sub 2}, N{sub 2}, and related ligands to [Mn(CO){sub 3}(PCy{sub 3}){sub 2}]{sup +} and other 16e electrophiles. N{sub 2} does not coordinate, and H{sub 2} is the most versatile weak ligand
- Univ. of Crete, Iraklio, Crete (Greece). Chemistry Dept.
- Los Alamos National Lab., NM (United States)
The photochemical reaction of Mn(CO){sub 5}Br with PCy{sub 3} in toluene proceeds with the fast evolution of CO. The complex formed, MnBr(CO){sub 3}(PCy{sub 3}){sub 2}, 1, readily reacts with NaA (A = B[C{sub 6}H{sub 3}(3,5-CF{sub 3}){sub 2}]{sub 4}) to form the dark green salt [Mn(CO){sub 3}(PCy{sub 3}){sub 2}][A], 2, which has an agostic interaction of a cyclohexyl C{single_bond}H with manganese. The light yellow {eta}{sup 2}-H{sub 2} complex, [Mn(H{sub 2})(CO){sub 3}(PCy{sub 3}){sub 2}][A], 3, forms at room temperature by placing solutions of 2 under 1 atm of H{sub 2}. The H{sub 2} ligand is labile and readily dissociates when the H{sub 2} atmosphere is removed in vacuo. {sup 31}P NMR clearly shows that at 25 C under 1 atm of H{sub 2}, 3 exists in equilibrium with 2. At {minus}78 C and under <1 atm of H{sub 2}, only 3 is observed. The synthesis of the new tricarbonyl complex [Mn(CO){sub 3}(PCy{sub 3}){sub 2}]{sup +} provides an excellent system of comparison for the binding of small molecules is similar known 16e fragments such as M(CO){sub 3}(PCy{sub 3}){sub 2} (M = Cr, Mo, W, Re{sup +}) and M(CO)(dppe){sub 2} (M = Mo, Mn{sup +}). The cationic manganese complex 2 appears to give somewhat more stable binding of H{sub 2} than the isoelectronic neutral chromium congener, which would not have been expected on the basis of relative back-bonding ability of the metal centers. Thus it is clear that increased {sigma}-donation more than compensates for decreased back-bonding in the relative metal-H{sub 2} bonding energies. Surprisingly, binding of N{sub 2}, ethylene, or silanes to 2 was not observed in solution even at low temperature and SO{sub 2} binds only weakly. By comparison with other similar systems, it is clear that H{sub 2} becomes an increasingly better ligand than N{sub 2} as the electrophilicity of the metal increases. Thus nonclassical H{sub 2} is a more versatile ligand than most classical ligands in its ability to adjust to a larger range of electronic situations.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); North Atlantic Treaty Organization, Brussels (Belgium); Los Alamos National Lab., NM (United States)
- OSTI ID:
- 315993
- Journal Information:
- Organometallics, Journal Name: Organometallics Journal Issue: 24 Vol. 17; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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