Osmium(VI) Nitrido and Osmium(IV) Phosphoraniminato Complexes Containing Schiff Base Ligands
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- 作者：Tsz-Wing Wong ; Tai-Chu Lau ; and Wing-Tak Wong
- 刊名：Inorganic Chemistry
- 出版年：1999
- 出版时间：December 27, 1999
- 年：1999
- 卷：38
- 期：26
- 页码：6181 - 6186
- 全文大小：97K
- 年卷期：v.38,no.26(December 27, 1999)
- ISSN：1520-510X
文摘
A series of osmium(VI) nitrido complexes containing Schiff base ligands, [OsVI(N)(L)Cl] (L = salophen or salen),have been synthesized by reaction of the ligand with [NBun4][OsVI(N)Cl4] in the presence of 2,6-dimethylpyridine.The 
(Os
N) for the salophen complexes occur at around 1070 cm-1 and are insensitive to the nature of thesubstituents present on the Schiff base ligand. The structures of [Os(N)(salophen)(MeOH)]ClO4 and [Os(N)(5,5-Cl2salophen)(MeOH)]ClO4 have been determined by X-ray crystallography, and the OsN bond distances are1.651 and 1.66 Å, respectively. The osmium(VI) nitrido complexes react rapidly with triphenylphosphine to producethe corresponding osmium(IV) phosphoraniminato complexes, [OsIV(NPPh3)(L)Cl]. The osmium(IV) complexesexhibit reversible OsV/IV and OsIV/III couples in cyclic voltammetry. The E1/2 values show linear correlations withthe Hammett constants 
p of the substituents on the Schiff base ligand. The structure of [OsIV(NPPh3)(salophen)Cl] has been determined by X-ray crystallography. The rather long Os-N(P) bond length (1.92 Å) and acuteOs-N-P bond angle (149.6
) suggest that there is no significant multiple-bond character in the Os-N bond.The kinetics of nitrogen atom transfer from a series of 5,5'-disubstituted salophen nitrido complexes to PPh3 havebeen studied in CH3CN at 25.0 C by stopped-flow spectrophotometric method. The following rate law wasobtained: -d[Os(VI)]/dt = k2[Os(VI)][PPh3]. The reactivities of the complexes were found to follow a Hammettcorrelation of log(kX/kH) with p, with a 
value of 1.9 ± 0.1. The positive value is consistent with a transitionstate involving electrophilic attack by the nitrido ligand on the phosphorus atom.
(OsN) for the salophen complexes occur at around 1070 cm-1 and are insensitive to the nature of thesubstituents present on the Schiff base ligand. The structures of [Os(N)(salophen)(MeOH)]ClO4 and [Os(N)(5,5-Cl2salophen)(MeOH)]ClO4 have been determined by X-ray crystallography, and the OsN bond distances are1.651 and 1.66 Å, respectively. The osmium(VI) nitrido complexes react rapidly with triphenylphosphine to producethe corresponding osmium(IV) phosphoraniminato complexes, [OsIV(NPPh3)(L)Cl]. The osmium(IV) complexesexhibit reversible OsV/IV and OsIV/III couples in cyclic voltammetry. The E1/2 values show linear correlations withthe Hammett constants p of the substituents on the Schiff base ligand. The structure of [OsIV(NPPh3)(salophen)Cl] has been determined by X-ray crystallography. The rather long Os-N(P) bond length (1.92 Å) and acuteOs-N-P bond angle (149.6) suggest that there is no significant multiple-bond character in the Os-N bond.The kinetics of nitrogen atom transfer from a series of 5,5'-disubstituted salophen nitrido complexes to PPh3 havebeen studied in CH3CN at 25.0 C by stopped-flow spectrophotometric method. The following rate law wasobtained: -d[Os(VI)]/dt = k2[Os(VI)][PPh3]. The reactivities of the complexes were found to follow a Hammettcorrelation of log(kX/kH) with p, with a value of 1.9 ± 0.1. The positive value is consistent with a transitionstate involving electrophilic attack by the nitrido ligand on the phosphorus atom.