Synthesis and Reactivity of Osmium and Ruthenium Vinylidene Complexes: Cleavage and Reconstruction of Carbon-Carbon Bond
Date Issued
2007
Date
2007
Author(s)
Cheng, Cheng-Wei
DOI
en-US
Abstract
The reactivity of a series of cationic metal (Os, Ru) vinylidene complexes containing the cyclopentadienyl(phosphine) and pentamethylcyclopentadienyl (phophine) ligand sets are discussed. The cationic metal vinylidene complexes 2 are prepared by alkylation reactions of alkyl halides with acetylide complexes (η5-C5R5)(PPh3)2M-C≡CR1 (1, M = Os, R = H, R1 = Ph; 1', M = Os, R = Me, R1 = Ph; 1a, M = Ru, R = H, R1 = Me; 1b, M = Ru, R = H, R1 = n-Bu). Complexes 2 react with n-Bu4NOH to yield (η5-C5R5)(PPh3)2M{C=C(R1)CHR2} 3 (cyclopropenyl complexes), which are observed during the cyclization process. However, only 3a (M = Os, R1 = Ph, R2 = CN), 3aa~3ac (M = Ru, R1 = Me, R2 = CN, Ph, CH=CH2) and 3bb (M = Ru, R1 = n-Bu, R2 = Ph) are isolated and the rest further transform into 4 (furan) or 5 (lactone) depending on the various group on vinylydene ligand of 2. Among all furan complexes 4, only 4e, 4ah, 4ch, 4ai, 4aj, 4ak and 4ck could further yield the lactone complexes 5e, 5ah, 5ch, 5ai, 5aj, 5ak and 5ck via sigmatropic rearrangements, respectively. The rate of rearrangement was affected by R1. The stability of the 3 in CHCl3 follows the trend for the substituents R1 of Ph ＞ Me ＞ n-Bu and for the substituents R2 of CN ＞ Ph ＞ CH=CH2.
The bimetallic compounds of [M1]=C=C(R1)CH2C(CH2R2)=C=[M2] (11, M = Os or Ru) containing a methylene bridge are prepared, but only complexes 11da (M1 = Os, M2 = Ru, R1 = Ph, R2 = CN) and 11db (M1 = Os, M2 = Ru, R1 = Ph, R2 = CO2Et) proceed to produce bismetallic cyclic complexes 12 and 13, respectively after deprotonation.
Using cationic osmium allenylidene complexes 14 and 14' with Grignard reagents R'CH2MgX, the acetylide complexes (η5-C5R5)(PPh3)2Os-C≡CC(Ph)2CH2R' are obtained. When they are further protonated by HBF4 in diethyl ether, corresponding vinylidene complexes [(η5-C5R5)(PPh3)2Os=C=CHC(Ph)2CH2R']+ (15, 15') are afforded. Most of complexes 15 are stable even in refluxing acetonitrile. Interestingly, two novel transformations are observed at ca. 50oC, including 15a (R = H, R' = CH=CH2) to [(η5-C5H5)(PPh3)2Os=C=CHCH2C(Ph)2(CH=CH2)]+ (17) caused by intramolecular metathesis process, and 15b (R = H, R' = C(Me)=CH2) to the cyclic allene complex 18 involved a C-C bond formation giving a six-membered ring and a change of coordination to a η2-allene mode. These similar transformations are also observed in ruthenium system (20'a → 22'a, 20'b → 26') in diethyl ether under low temperature (-20oC). The rates of the two transformations are closely related to the metallic fragments and the substituents at Cγ.
Replacing diethyl ether with MeOH, the reaction of 20'a and HBF4 affords an unsaturated cyclic carbene complex 23', which is fully characterized by single-crystal X-ray diffraction analysis. Unexpectedly, dissolving 22'a in MeOH also obtains the same product 23'. The reaction mechanism is elucidated by deuterium and 13C labeling experiments results and proposed to involve a skeletal rearrangement. For comparison, complex 22'a in iPrOH yields, besides 23', the corresponding alkoxycyclohexene 25c. Formation of 25c from 22'a also involves a skeletal rearrangement with reconstruction of the C=C bond. The proposed mechanism implicates a cyclobutylidene intermediate formed via either a regiospecific [2+2] cycloaddition of two double bonds in the ruthenium-vinylidene 22'a, or via a 5-endo cyclization of 22'a giving a nonclassical ion intermediate followed by a 1,2-alkyl shift.
Two types of cationic osmium and ruthenium vinylidene complexes, [(η5-C5R5)(PPh3)2M=C=C(R1)CH2R2] and [(η5-C5R5)(PPh3)2M=C=CHC(Ph)2CH2R'], were reported. By changing different alkylation group (R2), the former vinylidene complexes have been yielded various cyclic complexes (cyclopropene, furan and lactone). The reactivity of the other type [(η5-C5R5)(PPh3)2M=C=CHC(Ph)2CH2R']+ is closely related to the R' group.
Subjects
釕金屬,鋨金屬,亞乙烯基,環化反應,重排反應
ruthenium, osmium, vinylidene, cyclization, rearrangement
Type
thesis
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