Synthesis and Related Reactions of Ruthenium Vinylidene Complexes Containing a Pyridyl or a Terminal Vinyl Group

• Main Authors: Hsien-Hsin Chou, 周憲辛
• Other Authors: Ying-Chih Lin
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/99403324157754445136

博士 === 臺灣大學 === 化學研究所 === 96 === In this thesis, we investigated versatile reactivities of the half-sandwiched ruthenium acetylides, vinylidenes containing pyridyl or terminal vinyl group. We have prepared a series of ruthenium acetylides and vinylidenes containing pyridyl functional group. The ruthenium acetylides Cp(PPh3)2RuC≡C(C5H3RN) (R = H, 1a; Me, 1b) can undergo protonation, Lewis-acid interaction and alkylation to give the corresponding pyridiniumvinylidenes {Cp(PPh3)2Ru=C=C(H)(C5H3RNH)}+ (4a-4b) and pyridiniumacetylides Cp(PPh3)2RuC≡C(C5H3RN)→R’ (R’ = BF3 or BH3, 3a-3c; R’ = alkyl groups, 8a-8k), respectively. Both solution states of 3 and 4 will spontaneously decompose into the cationic alkoxycarbene complexes {Cp(PPh3)2Ru=C(O)CH2(C5H4N→BF2)}+ (6). These processes possibly involve an intermediate {Cp(PPh3)2Ru=C=C(H)(C5H3RN→BF2OH)}+ (5), which then undergo thermal rearrangement to yield alkoxycarbene complexes 6. The trace water in the solvent or in the ambient atmosphere appears to cause this decomposition. DFT calculations show that this transformation is a highly exothermic process (-23.09 kcal/mol). Some of the pyridiniumacetylides {Cp(PPh3)2RuC≡C(C5H3RNCH2R’)}+ (R = Me, R’= CO2Me, 8d; R = Me, R = Ph, 8i) can undergo further protonation to give pyridiniumvinylidene complexes {Cp(PPh3)2Ru=C=C(H)(C5H3RNCH2R’)2+ (9d, 9i). While complex 8g (R = Me, R’ = trans-CH=C(H)CO2Me) can undergo C-C coupling reaction of the acetylic β-carbon with alkylated olefin C=C double bond to give {Cp(PPh3)2Ru=C=C(C5H3RN)CH2CHCH2CO2Me}2+ (10a) in the air. Reactions of Cp*(PPh3)2RuCl with 2-ethynylpyridine or 2-cyanopyridine in the presence of KPF6 lead to formation of five-membered ruthenacyclic products Cp*(PPh3)Ru(κ2-C,N-C(H)=C(PPh3)(C5H4N))}PF6- (11a) and Cp*(PPh3)Ru(κ2-C,NNH)=C(OMe)(C5H4N))}PF6 (11b), respectively. Deprotonation of neutral vinylidenes Cp*(PPh3)(Cl)Ru=C=C(H)R (12a, R = Ph) in the presence of 2-electron donors give the neutral acetylides Cp*(PPh3)(L)RuC≡CPh (13a-13c, L = CO, PEt3, CNtBu). On the other hand, deprotonation of neutral vinylidenes 12a and 12b (R = nBu) in the presence of alkyl halides gives the asymmetric neutral vinylidenes Cp*(PPh3)(X)Ru=C=C(R)CH2R’ (14a-14g, R = Ph, nBu; X = Cl, Br; R’ = Ph, C6F5, C6H4-p-CN, CH=C(Me)2). The asymmetric cationic vinylidenes can be achieved via reaction of acetylides 13b and 13c with alkyl halides to give {Cp*(PPh3)(L)Ru=C=C(R)CH2R’}X (15a-15g, L = PEt3, CNtBu; R = Ph, nBu; R’= Ph, C6F5, C6H4-p-CN, CH=C(Me)2). A series of (pentamethylcyclopentadienyl)ruthenium vinylidene complexes {Cp*(L)2Ru=C=C(H)C(Ar)2CH2R}BF4 (20a-20l, L= PPh3, dppe; 2Ar = 2Ph, 2,2''-fluorenyl, 2(C6H4-p-OMe); R = CH=CH2, C(Me)=CH2, C≡CH, CH2CH2CH=CH2) was prepared. In chloroform complex {Cp*(PPh3)2Ru=C=C(H)C(Ph)2CH2CH=CH2}+ (20a) containing terminal vinyl group gradually transforms into {Cp*(PPh3)RuC(H)=C(PPh3)C(Ph)2CH2(η2-CH=CH2)}+ (25a) either at room or elevated temperature. Further monitoring indicates this transformation proceeds via formation of an intermediate {Cp*(PPh3)Ru(η2-HC≡C)C(Ph)2CH2(η2-CH=CH2)}+ (25a), which has been characterized by 2D NMR COSY and HSQC determination at 0oC. Addition of P(OPh)3 into solution of 25a give a mixture of 24a and another ruthenacyclic product {Cp*(P(OPh)3)RuC(H)=C(PPh3)C(Ph)2CH2(η2-CH=CH2)}+ (25c) in a ratio of 1:1.5. However, the methyl derivative 20a and 20h does not follow the same route. At room temperature the acetone solution of {Cp*(dppe)Ru=C=C(H)C(Ph)2CH2C(Me)=CH2}+ (20h) spontaneously transform into complex {Cp*(dppe)Ru(η2-C(H)MeC(H)=C=C(H)C(Ph)2CH2)}+ (27a) which containing coordinated cylic allene. In the presence of two-electron donors, such as P(OPh)3, CNtBu, acetonitrile or CO, complexes {Cp*(PPh3)2Ru=C=C(H)C(Ph)2CH2C(R)=CH2}+ (R = H, 20a; Me, 20b) in solution leads extrusion of 1,5-enyne ligands and {Cp*(PPh3)RuLL’}BF4 (22a-22d, L, L’ = P(OPh)3, CNtBu, NCMe, CO) were obtained. The more steric demanding Cp* ligand of these complexes probably plays important role in this phosphine dissociation-addition process, which was absent in the corresponding (cyclopentadienyl)ruthenium system. On the other hand, heating a THF solution of {Cp*(dppe)Ru=C=C(H)C(Ar)2CH2 CH=CH2}+ (20j, Ar = C6H4-p-OMe) at reflux give the skeletal rearrangement product {Cp*(dppe)Ru=C=C(H)CH2C(Ar)2CH=CH2}+ (28b). Deprotonation of the vinylidene complexes (28a-28b) causes acetylide complexes Cp*(dppe)RuC≡CCH2C(Ar)2CH=CH (Ar = Ph, 29a; Ar = C6H4-p-OMe, 29b). Further methylation of these acetylides give another vinylidene complexes {Cp*(dppe)Ru=C=C(Me)C(Ar)2CH=CH2}OTf (Ar = Ph, 30a). However, the vinylidene complex 30a is sufficiently stable toward rearrangement to give other products even under elevated temperature. Similar rearrangement process has earlier been experimentally observed in the Cp(PR3)2Ru system. Here we intend to theoretically analyze this rearrangement. DFT calculations show that this rearrangement is slightly exothermic for -1.55 kcal/mol, which possibly involves an ruthenium bicyclo[2.1.1]hexan-5-ylidene intermediate (Ibcl). Alternatively, another mechanism which involves formation of intermediates containing cyclohexenyl (Icy, Icy’) or fused-ring ligands (I35, I35’) has also been examined.