A “Lithium-Bonded” Cyclopropyl Edge:  The X-ray Crystal Structure of [Li−O−C(Me)−(c-CHCH₂CH₂)₂]₆ and Computational Studies

Abstract

The short Li-C distances (Li 1 -C 2 ) 2.615(3) Å, Li 1 -C 3 ) 2.644(3) Å) in the X-ray crystal structure of [Li-O-C(Me)-(c-CHCH 2 CH 2 ) 2 ] 6 (7) 6 characterize Li-cyclopropane edge coordinations. The Li-cyclopropane interactions increase the C 2 -C 3 distances (1.519(3) Å) relative to those of the free cyclopropyl edges (C 2 -C 4 ) C 6 -C 7 ) 1.499(2) Å) by 0.02 Å. The bent bonds of cyclopropane give rise to an electrostatic potential pattern, which strongly favors edge coordination as is observed experimentally in (7) 6 , but also permits a metastable Li + face complex. The cyclopropane edge also is the favored site for hydrogen bonding, but not for protonation. The C-C bond length elongations, the coordination energies E coord , and the charge redistributions upon metal cation edge interactions all are related to the distances between the cyclopropane C-C bond centers and the cations. This is evaluated for the alkali metal cation-cyclopropane complexes (cation ) Li + to Cs + ). More generally, the cyclopropane C-C bond length variations can be employed as a structural measure for the magnitudes of electrostatic interactions.

A Rhodium Complex with One Rh⋅⋅⋅CC and One Rh⋅⋅⋅HC Agostic Bond

“…Two possible mechanisms for this invoke a rhodium (v) Communications and calculations on the reaction of cyclopropane with a neutral {Cp*Rh(PMe 3 )} fragment [13,17] to form a rhodacyclobutane product suggest intermediates with a Rh I ···CC interaction, similar to that experimentally observed for 1; while complex 1 also has direct relevance to the recently reported catalytic carbon-carbon bond activation of cyclopropanes using [Rh(PPh 3 ) 3 Cl], [18] which is suggested to proceed through intermediates with Rh I ···CC interactions. Complex 1 decomposes in CH 2 Cl 2 solution over a period of 24 h, but is relatively stable in fluorobenzene (days, argon atmosphere).…”

“…[2] Complexes showing such M···CC interactions are extremely rare, and are limited to intramolecular (agostic) interactions that have been reported for complexes A-D; [3][4][5][6] although in one case (A) the bonding mode has been queried. [7] The lack of well-characterized examples of such species is in contrast with M···HC agostic complexes that are well established; [2,[8][9][10] and further examples of genuine, fully-characterized examples of M···C À C s interactions are of clear importance regarding the fundamental study of CÀC activation processes.…”

“…In solution, 1 reacts as if it were a source of Rh I coordinated with Binor-S (Scheme 4), suggesting that the cyclometalated Rh III species observed at low temperature and in the solid state is a resting state for a reactive {Rh(PiPr 3 )} + fragment. [19] Thus, reaction with simple Lewis bases such as CO and P(OPh) 3 gives free Binor-S and the rhodium(i) complexes [Rh(PiPr 3 )(CO) 3 ][BAr (3), [20] respectively. The solid-state structure of 2 reveals the expected square-planar Rh I species.…”

Probing the bent bonds in cyclopropane systems for gas storage and separation process: A computational study

“…The resulting hybridization for the ─C─H bonds were close to sp 2 , and the properties of these bonds strongly resemble those of ethylene . Cyclopropanes are cleaved by electrophiles, and in many cases protonation occurs both at the edge‐ and corners of these three‐membered rings . Like the π‐systems in unsaturated hydrocarbons, the cyclopropane “bent bonds” act as proton acceptors.…”

Synthesis and characterization of novel chelated dimethylamino lithium alkoxides: molecular structures of [1‐LiOC(C6H11)2‐2‐NMe2C6H4]2 and [1‐LiOCPh2CH2‐2‐NMe2C6H4]2

“…a THF-solvated dimer of lithium tert-butoxide. 4 Internal coordination by oxygen, 5 nitrogen, 6±13 phosphorus, 14,15 sulfur, 16 p-systems, 16±18 and cyclopropyl groups 19 have been identified in lithium alkoxides and show the diversity of the compounds. X-ray, NMR, and other techniques have confirmed a variety of different aggregate sizes of lithium alkoxides.…”