Eight-Coordinate Metal Carbonyls Containing Only Monodentate Ligands. Syntheses and Structural Characterization of [nPr4N]2[(Ph3Sn)4M(Co)4], M = Zr, Hf
✍ Scribed by Prof. John E. Ellis; Kai-Ming Chi; Dr. Anthony-J. DiMaio; Scott R. Frerichs; Jason R. Stenzel; Prof. Arnold L. Rheingold; Brian S. Haggerty
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 394 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0044-8249
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✦ Synopsis
four coordinate 4, and five coordinate 5 have identical g, and g,l to 2. UV-vis spectra show that 5 does not dispropor-[Ni(C6H,CH=N-NHCSNH2),1C1Z 4 [Ni(C,H,OHCH=N-NHCSNH,)(C,H,CH="HCSNHCSNHz)]Clz 5 tionate to 1 and 4. The Nil complexes are therefore fourcoordinate with an N,S, environment.
We looked at DJH exchange with ethanol-OH protons catalyzed by 1. Exposure to D, (1 atm) gave H/D exchange, especially in the presence of promoters like HI or HBF,. A 0.1 M solution of 1 in a dimethyl sulfoxide/ethanol mixture (90:lO) gave 7.5 turnoversf2'' of H/D exchange after five minutes at 25 "C and 1 atm pressure of D,. Deuteriation of the EtOH proton was followed by 2D NMR by monitoring the EtOD resonance at 6 = 4.15 versus C,D, as standard. The catalytic activity disappeared after 7.5 turnovers. Neither 4 nor 5 promotes H/D exchange, so both phenolic OH groups are required for activity. A possible catalytic intermediate is 3,[261 in which one phenol group is bound to the nickel, and the other forms a hydrogen bond with H, (Scheme 1). Hydrogen bonding may increase the affinity of the complex for H, and promote exchange (Scheme 2). This work reveals some unusual features of Ni chemistry in an S-donor environment. A stable Nil species is formed from 1 on reduction. In solution, ligand dissociation leads to a species which interacts with D, and promotes H/D exchange. Compound 1 is thus a functional model for hydrogenases.