Synthesis and structural characterization of group 6 transition metal complexes with terminal fluoromethylidyne (CF) ligands; a DFT/NBO/NRT comparison of bonding characteristics of terminal NO, CF and CH ligands

Abstract

A family of group 6 transition metal complexes M(C(5)R(5))(CO)(2)(CF) [M = Cr, Mo, W; R = H, Me] with terminal fluoromethylidyne ligands have been synthesized through the reduction of the corresponding trifluoromethyl precursors with potassium graphite or magnesium graphite. They have been characterized spectroscopically and in some cases crystallographically, although the structures show disorder between the CO and CF ligands. The M[triple bond]CF subunit reacts as a triple bond to form cluster complexes containing μ(3)-CF ligands on reaction with Co(2)(CO)(8). Computational (DFT/NBO/NRT) studies on M(C(5)H(5))(CO)(2)(CF) [M = Cr, Mo, W] and the corresponding cationic fragments M(CO)(2)(XY)(+) illustrate significant differences in the metal-ligand bonding between CF and its isoelectronic analogue NO, as well as with its hydrocarbon analogue CH.

Proton Affinities of Cationic Carbone Adducts [AC(PPh3)2]+(A=Halogen, Hydrogen, Methyl) and Unusual Electronic Structures of the Cations and Dications [AC(H)(PPh3)2]2+

“…An exactly planar arrangement is found around the central carbon atom C(1), pointing to a filled p orbital and sp 2 hybridization. A rather long C−F bond length of 1.421 Å (mean value) in 1 F + contrasts with the short one of 1.291 Å in a related NHC‐F cation; the latter is in the range of terminally bonded CF ligands in transition‐metal complexes . Typical C−F bond lengths, for example, in the anion (CF 3 SO 3 ) − are found to be about 1.340 Å or in transition‐metal complexes with a bridging CF 2 ligand .…”

“…An exactly planar arrangement is found aroundt he central carbon atom C(1), pointing to af illed po rbital and sp 2 hybridization.Ar ather long CÀFb ond length of 1.421 ( mean value) in 1F + + contrasts with the short one of 1.291 i narelated NHC-F cation; [31] the latter is in the range of terminally bondedC Fl igands in transition-metal complexes. [32] Typical CÀFb ond lengths, for example, in the anion (CF 3 SO 3 ) À are found to be about 1.340 o ri nt ransition-metal complexes with ab ridging CF 2 ligand. [33] Thel one pair of electrons of p symmetry at C(1) probablye xperiences somer epulsion from the related filled po rbitals at the Fa tom, whereas in the NHC-F + cation some CÀFd ouble bond character through back-bonding into av acant po rbital of the carbon atom is operative.…”

The Trifluoromethyl Group in Transition Metal Chemistry

“…The difluorocarbene–metal unit, [M]=CF 2 , that results from fluoride abstraction generally shows such a rich reactivity that a high synthetic potential can be associated with this process. The recently described two‐electron reduction of [M]–CF 3 compounds with potassium or magnesium graphite to give the corresponding [M]≡CF derivatives is also of prominent importance 164. The syntheses of additional transition metal compounds containing the unusual fluoromethylidyne ligand as well as the development of its chemical reactivity also appear very promising.…”

Influence of spacer group substituent on mesomorphism in copper complexes of ‘salen’ type Schiff bases bearing long alkoxy arm

“…Appropriate structures were confirmed as energy minima by calculating the vibrational frequencies using second derivative analytic methods, and confirming the absence of any imaginary frequencies. [51] For Cu 2+ complexes, which are open-shell systems, the expectation value showed that the spin contamination of the unrestricted wave function was always very small. [52] All DFT calculations were carried out with the Gaussian 09 programs.…”