A Π-Adduct of Chromocene: (η⁵-C₅H₅)₂Cr(η²-C₄F₆)

ansa-metallocene derivatives

“…The Cr-C(ring) distances are identical within standard deviations; their mean value of 216 ± 1 pm is in close agreement with a value of 216.9(0.4) pm observed for (CsHshCr by gas phase electron diffraction [8]. The centroid-metal-centroid angle is 143.3°, substantially larger than the angles of 128 and 130° observed in ethylene- Cr-C(I) 217(1) Cr-C(6) 214(1) Cr-C (2) 216(1) Cr-C(7) 217(1) Cr-C 3214 1Cr-C(8) 218(1) Cr-C 4216 1Cr-C(9) 213(1) Cr-C (5) 218 ( bridged [9) and in unbridged titanocene dichloride [10), but quite close to a centroid-metal-centroid angle of 145.8 0 observed for (CsHshMoH2 [11]. Although not fixed by crystallographic site symmetry, the structure depicted in Fig.…”

“…Later, we found that (CsHshCr is quantitatively converted to the diamagnetic adduct (CsHshCr(CO) by reaction with CO in pentane at -78°C [4]; at room temperature, however, the CO dissociation pressure rises above 100 mbar. Finally, Chisholm et al reported that F 3 CC=CCF 3 to form a diamagnetic (CSHS)2Cr adduct at temperatures below -30°C; at room temperature, this complex is converted into an incompletely characterized paramagnetic material [5]. We now report the synthesis and molecular structure of a surprisingly stable carbonyl derivative of an ansa-chromocene containing an interannular tetramethylethylene bridge.…”

ansa-Chromocene Complexes. 1. Synthesis and Characterization of Cr(II) Carbonyl and tert-Butyl Isocyanide Complexes

“…We hope to use the electrochemical behavior of the ansa -chromocene complexes as a guide in exploring the reactivity of these systems. Much of the interesting chemistry exhibited by the heavier tungstenocene and molybdenocene congeners involves the metals in their formally +4 oxidation states; 2c,d,22a-d thus, we are interested in accessing this formal oxidation state in our ansa -chromocene systems. Brintzinger and co-workers have already demonstrated that the interannular bridge has a pronounced effect on the redox properties of 2a as compared with the parent chromocene carbonyl complex .…”

“…Bent-sandwich dicyclopentadienyl complexes of the early transition metals from groups 3−6, with the exception of chromium, have exhibited a rich and varied chemistry that continues to be useful for homogeneous catalysis, organic synthesis, and the elucidation of organometallic reaction mechanisms. The chemistry of bent-sandwich chromocene has eluded chemists largely due to the reluctance of 16e - Cp 2 Cr to coordinate ligands such as CO, which cause it to adopt a bent-sandwich geometry, and the propensity of chromocene toward cyclopentadienyl ring loss. 2a-d No bona fide bent chromocene derivative had been characterized until 1982, when Brintzinger and co-workers reported the synthesis, X-ray crystal structure, and chemical properties of ansa -Me 4 C 2 (C 5 H 4 ) 2 CrCO . The presence of an interannular tetramethylethano bridge is crucial to the stability of this species, which, unlike the parent complex, Cp 2 CrCO, retains its coordinated carbonyl in the absence of a CO overpressure.…”