Reaction of cationic cyclobutadineruthenium complexes with hydride anion donors; evidence for the formation of η4(5e) butadienyl species and fragmentation of the cyclobutadiene ring: crystal structure of [RuC(Ph)–η3-{C(Ph)·CH(Ph)·CH(Ph)}-(η-C5H5)] and [Ru2(µ-CO){µ-(Z)-C(Ph)CH(Ph)}(CO)2(η4-C4Ph4)(η-C5H5)]
“…However, despite many similarities between them, the principal difference results from the much easier ability of the coordinated cyclobutadiene ligand (as compared with Cp) to convert into other ligands. This is clearly demonstrated by recently described protonation of complex 5a to give the allyl carbene complex [CpCo(σ,η 4 -C 4 HMe 4 )] + with a five-electron butadienyl ligand, , which rearranges to produce the half-open cobaltocenium cation [CpCo(η 5 -C 5 H 4 Me 3 )] + . 4 …”
Tetramethylcyclobutadiene(cyclopentadienyl)cobalt complexes Cb*Co(C 5 H 4 R) (Cb* ) η 4 -C 4 Me 4 ; R ) H (5a), Me (5b), SiMe 3 (5d), C(O)H (5f), and C(O)Me (5g)) were obtained by reaction of cyclopentadienide anions either with the (carbonyl)iodide complex Cb*Co(CO) 2 I (1) (method A) or with the more reactive acetonitrile complex [Cb*Co(MeCN) 3 ] + (2) (method B). Analogous compounds Cb*CoCp* (5c), Cb*Co(1,3-C 5 H 3 (SiMe 3 ) 2 ) (5e), and Cb*Co(η 5indenyl) (6) can be prepared only by method B. Treatment of 5f,g with NaBH 4 /AlCl 3 or LiAlH 4 affords the alkyl derivatives 5b and 5h (R ) Et) or the alcohols 5i (R ) CH 2 OH) and 5j (R ) CH(OH)Me), respectively. The reaction of 1 with fluorene/AlCl 3 yields complex [Cb*Co-(η 6 -fluorene)] + (8), which was deprotonated by KOBu t to give Cb*Co(η 6 -fluorenyl) (9). Visible light irradiation of 9 induces η 6 fη 5 haptotropic rearrangement to afford Cb*Co(η 5 -fluorenyl) (7). The pyrrolyl and phospholyl complexes Cb*Co(C 4 R 4 N) (R ) H (10a), Me (10c)) and Cb*Co-(C 4 R 4 P) (R ) H ( 11a), Me (11c); R 4 ) H 2 Me 2 (11b)) were obtained by reaction of 2 with the corresponding pyrrolide or phospholide anions. Improved procedures for the preparation of the starting materials 1 and 2 were developed. Using a one-pot procedure, the iodide 1 was obtained in high yield from 2-butyne and Co 2 (CO) 8 . Complex 2 was prepared by heating or irradiation of the toluene complex [Cb*Co(C 6 H 5 Me)] + (4b) in acetonitrile. Structures of 5g, 6, and 11c were investigated by X-ray diffraction. Electrochemistry and joint UV-visible and EPR spectroelectrochemistry of complexes prepared were studied.
Scheme 3Scheme 4
“…However, despite many similarities between them, the principal difference results from the much easier ability of the coordinated cyclobutadiene ligand (as compared with Cp) to convert into other ligands. This is clearly demonstrated by recently described protonation of complex 5a to give the allyl carbene complex [CpCo(σ,η 4 -C 4 HMe 4 )] + with a five-electron butadienyl ligand, , which rearranges to produce the half-open cobaltocenium cation [CpCo(η 5 -C 5 H 4 Me 3 )] + . 4 …”
Tetramethylcyclobutadiene(cyclopentadienyl)cobalt complexes Cb*Co(C 5 H 4 R) (Cb* ) η 4 -C 4 Me 4 ; R ) H (5a), Me (5b), SiMe 3 (5d), C(O)H (5f), and C(O)Me (5g)) were obtained by reaction of cyclopentadienide anions either with the (carbonyl)iodide complex Cb*Co(CO) 2 I (1) (method A) or with the more reactive acetonitrile complex [Cb*Co(MeCN) 3 ] + (2) (method B). Analogous compounds Cb*CoCp* (5c), Cb*Co(1,3-C 5 H 3 (SiMe 3 ) 2 ) (5e), and Cb*Co(η 5indenyl) (6) can be prepared only by method B. Treatment of 5f,g with NaBH 4 /AlCl 3 or LiAlH 4 affords the alkyl derivatives 5b and 5h (R ) Et) or the alcohols 5i (R ) CH 2 OH) and 5j (R ) CH(OH)Me), respectively. The reaction of 1 with fluorene/AlCl 3 yields complex [Cb*Co-(η 6 -fluorene)] + (8), which was deprotonated by KOBu t to give Cb*Co(η 6 -fluorenyl) (9). Visible light irradiation of 9 induces η 6 fη 5 haptotropic rearrangement to afford Cb*Co(η 5 -fluorenyl) (7). The pyrrolyl and phospholyl complexes Cb*Co(C 4 R 4 N) (R ) H (10a), Me (10c)) and Cb*Co-(C 4 R 4 P) (R ) H ( 11a), Me (11c); R 4 ) H 2 Me 2 (11b)) were obtained by reaction of 2 with the corresponding pyrrolide or phospholide anions. Improved procedures for the preparation of the starting materials 1 and 2 were developed. Using a one-pot procedure, the iodide 1 was obtained in high yield from 2-butyne and Co 2 (CO) 8 . Complex 2 was prepared by heating or irradiation of the toluene complex [Cb*Co(C 6 H 5 Me)] + (4b) in acetonitrile. Structures of 5g, 6, and 11c were investigated by X-ray diffraction. Electrochemistry and joint UV-visible and EPR spectroelectrochemistry of complexes prepared were studied.
Scheme 3Scheme 4
“…These molecules show low-field 13C resonances due to the q2-vinyl fragment; however, in contrast with the parent (+ 0.5) kJ mol-11 in the dichloro-complex (7). It was confirmed that in the formation of (7)-( 9) from (4)-( 6), coupling of the y2(3e)-vinyl and y2-alkyne ligands had not occurred because when (7)-( 9) were treated with AgBF4, a precipitate of AgX was produced and the parent cations (4)- (6) were reformed in good yield. In contrast, linking of the q2-vinyl and but-2-yne ligands does occur on treatment of, for example, (4) with trimethyl phosphite and (6) with trimethylphosphine.…”
mentioning
confidence: 82%
“…It was confirmed that in the formation of (7)-( 9) from (4)-( 6), coupling of the y2(3e)-vinyl and y2-alkyne ligands had not occurred because when (7)-( 9) were treated with AgBF4, a precipitate of AgX was produced and the parent cations (4)- (6) were reformed in good yield. In contrast, linking of the q2-vinyl and but-2-yne ligands does occur on treatment of, for example, (4) with trimethyl phosphite and (6) with trimethylphosphine. In both reactions orange crystalline products are formed, the reaction with P(OMe)3 and (4) giving (lo), and PMe3 and (6) affording two isomeric complexes of (11) in the ratio of (6: 1).…”
Protonation (HBFd.Et20) of [ M O X ( ~~-M ~C ~M ~) ~L ] (X = CI, Br, I; L = q-C5H5 or q5-C9H7) affords the cations [XM-HMe(q2-MeC2Me)Ll [BF41, which react with LiX to give [X2klo=C(Me)~HMe(q2-MeC2Me)L] or with PR3 (R = Me, or OMe) to give the C-C coupled products [XMo=C(Me)-q3-{C(Me)C(Me)CHMe}(PR3) (L)][BF4], the latter being structurally identified by X-ray crystallography; carbon-carbon coupling also occurs on reduction of [Br2M-HMe(q2-MeC2Me)(q-C5H5)] with Mg/Hg in the presence of CO to form [MoBr(CO){q4-CHMe=C-(Me).C(Me)=CHMe}(q-C5H5)l, and treatment of the phosphine promoted coupled products with Li[N(SiMe3)2] leads to reversible deprotonation reactions affording [MoX{q4-CHMe=C(Me).C(Me)=C=CH2}(PR3)L].
“…This apparent stereomutation reaction is unusual and may be related to the isomerisation of butadienyldithiocarbamatepalladium complexes reported by Maitlis and Taylor3 and interpreted in terms of a ring-flip process. It was clearly important to examine whether the transformation of (1) to (3) could be reversed by thermal expulsion of P(OMe)3, because if this was successful it would have implications for the synthesis of other a,q3(5e)-butadienyl species. However, in the event a new reaction intervened.…”
o,q3(5e)-Butadienylruthenium complexes behave as masked ofq*(3e)-butadienyl complexes in their reactions with P(OMe)3 and PhC2Ph, whereas, protons react on the 'inside' of the o,ys-butadienyl chain at the a-carbenoid carbon; attempts to expel P(OMe)3 thermally from the resulting o,q*(3e)-butadienyl complexes results instead in a zeta-H abstraction reaction.Recently' we described a study of ring-opening reactions of (2). Not only are these molecules interesting from a bonding cationic y4-cyclobutadiene complexes, which led to the viewpoint, but they are also potentially reactive. This reaccharacterisation of the first examples2 of a,q3(5e)-butadienyl tivity might be expected to be associated with the metal-tocomplexes [Ru=C(Ph)-q3-{ C(Ph)C(Ph)CH(Ph)}(q-CsHs)] carbon multiple bond. In addition the possibility that these (1) and [Ru=C(Ph)-q3-(C(Ph)C(Ph)C(Ph)CHO} (q-CsHs)]
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