Kinetic studies of the reactions of the carbene complex W(CO)5[C(SCH3)2] with phosphines to form phosphorane complexes W(CO)5[(CH3S)2C-PR3] and the synthesis of some cyclic phosphorane complexes |
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| Authors: | Ruth A. Pickering Robert J. Angelici |
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| Affiliation: | Department of Chemistry and Ames Laboratory — USDOE, Iowa State University, Ames, Iowa 50011 U.S.A. |
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| Abstract: | ![]()
The dithiocarbene complex W(CO)5[C(SCH3)2 reacts with tertiary phosphines, PPh2CH3, PPh(CH3)2, P(C2H5)3 and P(OCH3)3 to form the phosphorane complexes W(CO)5[CH3S)2C-PR3] and with HPPh2 to form the phosphine complex W(CO)5[PPh2[CH(SCH3)2]. Kinetic studies of both types of reactions show that their rates are first order each in W(CO)5[C(SCH3)2] and in the phosphorus ligand. A mechanism involving rate determining phosphorus attack at the carbene carbon followed by rapid rearrangement to the product is consistent with this rate law. Rate constants for the reactions increase with increasing nucleophilicities of the phosphines: P(OCH3)3 < PPh2H < PPh2CH3 ? PPh(CH3)2 < P(C2H5)3. The ΔH values decrease (P(OCH3)3 > PPh2H > PPh2(CH3) > PPh(CH3)2 > P(C2H5)3) as the nucleophilicities of the phosphines increase. The ΔS values (≈-30 e.u.) remain essentially constant for all the reactions. The cyclic dithiorcarbenes W(CO)5[CS(CH2)nS], wheren- 3 or 4, react with PPh2(CH3) to form the cyclic phosphorane complexes, W(CO)5[S(CH2)nSC-PPh2(CH3)]. The 6- and 7- membered cyclic dithiocarbenes also react with PPh2H to form the phosphine complexes, W(CO)5 {PPh2- [CS(CH2)nS(H)]}. |
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