Photoinduced [6 + 2] cycloadditions of alkynes to tricarbonylcycloheptatrienechromium(0)

Cycloheptatriene and -enyl Complexes of the Early Transition Metals

“…The ion C7H8Cr+ has an anomalously low reactivity which has been explained by a /3-hydride shift from the cycloheptatriene ring to the chromium atom that decreases the electron deficiency on the central metal. It was reported that lithiation of the sandwich compound TilV^HvX^-CsHs) (80) occurs preferentially at the seven-membered ring. Addition of electrophile to the resulting lithiated species leads to selective functionalization of the cycloheptatrienyl ligand.57 Thus treatment of 80 with 1 equiv of n-butyllithium in ether followed by the addition of 1 equiv of PPh2Cl affords the phosphine containing titanium compound 81 (Scheme 40).…”

Photoreactions of Chromium Cyclodienyl Complexes with Alkynes: Double [5 + 2],homo[5 + 2] Cycloaddition Reactions

“…Within this field, significant advances have been made in the construction of medium-size carbo- and heterocyclic rings through transition metal-mediated higher-order cycloaddition processes. − For example, Rigby and co-workers have extensively investigated photoinduced [6 + 2] and [6 + 4] cycloadditions using [(η 6 -triene)Cr(CO) 3 ] complexes and olefins, dienes, , heterocumulenes, or even transition metal carbene complexes . Likewise, we , and others have demonstrated the related chromium-mediated [6 + 2] cycloadditions of alkynes to trienes.…”

Synthesis, molecular and crystal structure of a tricarbonylchromium complex of 7-(2-phenyl-o-carboran-1-yl)cyclohepta-1,3,5-triene

“…2,3 Tricarbonylchromium complexes of substituted cycloheptatrienes can also be involved in the reaction. 4,5 The complexes can be prepared by reactions of a tropylium tricarbonylchromium complex with the corresponding nucleophiles. 6 Their tricarbonylchromium complexes can also enter the reactions, and the cycloaddition products obtained differ in structure from those prepared from the uncomplexed starting cyclohepta-1,3,5-triene derivatives.…”

“…The intensities of 3426 reflections were measured on a Siemens P3/PC diffractometer at -120 °C (λMoKα radiation, q/2q scan technique, 2q < 50°), and 3048 independent reflections were used in further calculations and refinement. The absolute conformation for the molecule of 4b was determined by calculation of the Flack parameter [k = 0.05 (5)]. The structure was solved by a direct method and refined by a full-matrix least-squares technique against F 2 in an anisotropic-isotropic approximation.…”