Organometallics 1989,8, 1803-1805
1803
A Sandwich Complex Containing Trimethylenemethane, (q4-2-Methylene4,3-propanediyl) (q5-2,4-cyclopentadien-l-yl)cobalt R. Scott Lokey and Nancy S. Mills" Department of Chemistry, Trinity University, San Antonio, Texas
Arnold
L. Rheingold
Department of Chemistty, University of Delaware, Newark, Delaware 19716 Received February 27, 1989
(q!-2-Methylene-l,3-propanediyl) (q5-2,4-cyclopentadien-l-yl)cobalt (TMMCoCp)was prepared by reaction diiodide. TMMCoCp of dilithioisobutylene with (~5-2,4-cyclopentadien-l-yl)(triphenylphosphine)cobalt was characterized spectroscopically ('H and 13C NMR, IR, mass, and UV/vis spectroscopy) and by a crystal structure (monoclinic, P2,/n, a = 6.057 (2) A, b = 7.890 (1)A, c = 8.813 (2) A, p = 93.04 ( 2 ) O , V = 415.3 (2) A3, 2 = 2; for 553 observed reflections, RF = 5.27%.) The complex, which is isoelectronic with (q4-1,3-cyclobutadiene)(q5-2,4-cyclopentadien-l-yl)cob~t, is the first neutral trimethylenemethane complex of cobalt and is the simplest trimethylenemethane mixed-sandwich complex reported to date. Cyclic voltammetry of TMMCoCp in acetonitrile showed a single irreversible wave on the anodic scan. Initial examination of its chemistry revealed that metalation with n-butyllithiumlTMEDA occurred exclusively on the trimethylenemethane ligand. Scheme I We have been involved for some time with the question of Y-aromaticity' in delocalized dilithiated hydrocarbons.2 The ease of preparation of many of these species suggested that they might be useful synthetic precursors to novel molecules, and we have been investigating their applicability in the synthesis of organometallic compounds. As shown in Scheme I, we have considered dianions such as the dianion of isobutylene as a 6a-electron donor capable of reaction with metal dihalides to give either metallocyclobutanes or trimethylenemethane compounds, deIVlL" pending on the metal dihalide and its ligands. As further guidance, we considered that cyclobutadiene transitionmaterial. We have also reacted the dianion of isobutylene metal complexes might serve as models for potentially with carbonyl(~5-2,4-cyclopentadien-l-yl)diiodocobalt3 successful syntheses with delocalized cross-conjugated which results in the synthesis of TMMCoCp in similar dianions. One might consider those complexes as conyield. taining dianionic 6a-electron cyclobutadiene ligands, aroTMMCoCp was characterized spectroscopically and its matic in the Huckel sense, which would be isoelectronic identity confirmed by a crystal structure. The 300with the potentially Y-aromatic 6a-electron dianion of MHz-IH NMR spectrum in C6D6 showed two singlets, a t isobutylene. 4.73 and 1.79 ppm, with integration respectively of 5:6 We now report the successful preparation of ( ~ ~ - 2 - protons. The analogous (q4-1,3-cyclobutanediene)(q5-2,4methylene-1,3-propanediyl) (~$'-2,4-cyclopentadien-l-y1)cyclopentadien-1-yhobalt (CbCoCp) showed a resonance cobalt (TMMCoCp) from reaction of the dianion of isoa t 4.86 ppm for the cyclopentadienyl protons as well as a butylene prepared as previously reported2 by dimetalation resonance a t 3.61 ppm for the equivalent cyclobutadiene of isobutylene with n-butyllithium/N,N,N',N'-tetraproton^.^ The l3cNMR spectrum in CsD6of TMMCoCp methylethylenediamine (TMEDA), with 1 molar equiv of showed resonances a t 81.76 ppm from TMS for the cy(q5-2,4-cyclopentadien-1-yl)diiodo(triphenylphosphine)coclopentadienyl carbons (compared with 83.4 ppm for the balt.3 This represents the first report of a neutral tricyclopentadienyl carbons of (q4-1,2,3,4-tetraphenyl-1,3methylenemethane complex of cobalt as well as the prepcyclobutadiene)(q5-2,4-cyclopentadien-l-yl)cobalt5), at aration of the simplest mixed-sandwich trimethylene44.99 ppm for the trimethylenemethane methylene carmethane complex. The reaction, run in T H F a t -78 "C, bons, and a t 112.25 ppm for the central carbon of the resulted in the formation of TMMCoCp as reddish brown, trimethylenemethane ligand. GC/mass spectral analysis air-stable crystals in 18% (isolated) yield. The majority showed three major fragmentations: m/charge 178 (51% of the reaction mixture was pentane-insoluble and conabundance) for the parent ion, 124 (100%) from loss of the tained paramagnetic materials. We believe that reduction TMM ligand, and 59 (70%) from loss of the cyclovia electron transfer from the isobutylene dianion to the pentadienyl ligand. This fragmentation may be compared cobalt starting material is responsible for the paramagnetic to that of the isoelectronic CbCoCp4 in which the major (1) Finnegan, R. A. Ann. N . Y.Acad. Sci. 1969, 152, 242. Rajca, A.; Tolbert, L. M. J. Am. Chem. SOC. 1985,107,698. Agranat, I.; Skancke, 1985, 107, 867. A. J . Am. Chem. SOC. (2) Mills, N. S.; Shapiro, J.; Hollingsworth, M. J. J. Am. Chem. SOC. 1981, 103, 263. Mills, N. S.; Rusinko, A. R.; J. Org.Chem. 1986,51, 2567. A 1971, 3173. King, R. (3) Roe, D. M.; Maitlis, P. M. J . Chem. SOC. B. Inorg. Chem. 1966,5, 82.
(4) Amiet, R. G.; Pettit, R. J . Am. Chem. SOC.1968, 90,1059. (5) Seyferth, D.; Merola, J. S. J . Organomet. Chem. 1978, 162, C35. (6) The UV/vis spectrum in pentane shows maxima a t 219,257, and 440 nm (e = 17 141, 14 110, and 876). T h e crystals are thermochromic, turning yellow a t -196 "C from their reddish-brown coloration a t room temperature.
0276-7333/89/2308-1803$01.50/00 1989 American Chemical Society
1804 Organometallics, Vol. 8, No. 7, 1989
Lokey et al.
Table I. Principal Infrared Absorptions of Ferrocene, (Trimethylenemethane)(cyclopentadienyl)cobalt, (Trimethy1enemethane)ironTricarbonyl, and (Cyclobutane)(cyclopentadienyl)cobalt Cp,Feojb 3084 1407 1101 999 CpCo(TMM)" 3113 3067 2997 1477 1442 1415 1385 1107 1000 979 805 (C0)3FeTMMc 3067 3000 1478 1456 1349 989 803 CpCoCB" 3090 3060 1408 1101 997
787 784
"Determined in KBr. *Rosenblum, M.; North, B.; Wells, D.; Giering, W. P. J . Am. Chem. SOC.1972, 94, 1239. CEmerson,G. F.; Ehrlich, K.; Giering, W. P.; Lauterbur, W. P. J . Am. Chem. SOC.1966,88, 3172.
Figure 1. The molecular structure of CpCo(C4H6)constructed from an end-for-end inversionally disordered model: Co-Cp(cent), 1.584 (8);CO-C(l), 1.891 (8);Co-C(2), 2.052 (8);co-c(7)2.251 (9); CoC(S), 2.048 (7); C(1)
