(Tetramethylcyclobutadiene)cobalt Complexes with Five-Electron Carbo- and Heterocyclic Ligands

Abstract

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

(Tetramethylcyclobutadiene)cobalt Complexes with Tricarbollide Ligands

“…The Co···Cb* distances in complexes 4a (1.696 Å) and 7b (1.703 Å) are slightly longer than that in Cb*Co(η-C 5 H 4 COMe) (1.683 Å) [3] but shorter than in Cb*Co[1a] (1.712 Å) and Cb*Co[1c] (1.711 Å), [1] suggesting that the tricarbollide ligands 2a and [1-tBuNH-1,7,9-C 3 B 8 H 10 ]…”

“…The isolation of products was conducted in air. Starting materials were prepared as described in the literature: Cb*Co(CO) 2 I, [3,13] [Cb*Co(C 6 H 6 )]PF 6 , [3,13] [Cb*Co(MeCN) 3 ]PF 6 , [3,13] […”

“…[2,3] One method is based on the reaction of the (carbonyl)iodide complex Cb*Co(CO) 2 I with the corresponding anions, while another one uses the acetonitrile complex [Cb*Co-(MeCN) 3 ] + as a starting material. The second method is more general, allowing Cb*Co(C 4 R 4 E) compounds to be synthesized in higher yields under milder conditions.…”

Slipped μ‐Indenyl Triple‐Decker Complexes Containing (C4Me4)Co and (C5R5)Ru Fragments

“…[10][11][12][13] The acetonitrile complex [Cb*Co(MeCN) 3 ] + (Cb* = C 4 Me 4 ) has been shown to be the most useful synthon of the Cb*Co fragment. In particular, its reaction with the indenide anion gives the η 5 -indenyl derivative [Cb*Co(η 5 -C 9 H 7 )] (1).…”

“…In particular, its reaction with the indenide anion gives the η 5 -indenyl derivative [Cb*Co(η 5 -C 9 H 7 )] (1). [12] Herein we describe the synthesis and electrochemical behaviour of dicobalt and cobalt-ruthenium triple-decker complexes with a bridging indenyl ligand. [14] Results and Discussion…”