Structural Dichotomy in Six-Coordinate d⁰ Complexes:  Trigonal Prismatic (^tBu₃SiC⋮C)₆Ta^- and Octahedral (^tBu₃SiC⋮C)₆M^2- (M = Zr, Hf)

Abstract

, and 7 (O h ). The D 3h to D 3 twist in 3 and 5 has a steric origin, and the counterion position appears inconsequential. Origins of the structural preferences illustrated by the dichotomous twisted trigonal prismatic and octahedral cores of the d 0 hexaacetylides 5 and 6 were probed through density functional (ADF) and effective core potential (GAMESS) calculations. The structural difference results from a lessening electronic preference for the trigonal prismsprimarily a greater HOMO/LUMO gapsupon moving from Ta to Zr, minor steric factors, and increased interligand repulsions in the dianion (VSEPR).

Synthesis, structure and bonding of hexaphenyl thorium(iv): observation of a non-octahedral structure

“…[1][2][3][4][5] In particular, the observation of a trigonal prismatic structure for these complexes, as opposed to the more common octahedral geometry, is considered strong evidence for the involvement of the d orbitals in the metal-carbon bonds. 2, 3 A number of trigonal prismatic [MR 6 ] qtype complexes have been structurally characterized, including [Li(TMEDA)] 2 [Zr(CH 3 ) 6 ], 6 [M(CH 3 ) 6 ] q (M = W, Re, Nb, Ta; q = 0,À1), 4 [Ta(CRCSitBu 3 ) 6 ] À , 7 [M(C 6 H 5 ) 6 ] 2À (M = Zr, Nb), 8 and [Ta(C 6 H 5 ) 6 ] À . 9 Notably absent from this list, however, are their heavier actinide analogues.…”

“…Its 1 H NMR spectrum in THF-d 8 at RT reveals resonances at 7.61 ppm, 7.00 ppm and 6.79 ppm in the ratio of 2 : 2 : 1, corresponding to the ortho, meta, and para protons of the phenyl ring, respectively. In addition, there is a single resonance in its 7 Li{ 1 H} NMR spectrum at 2.60 ppm. The 13 C{ 1 H} NMR spectrum in THF-d 8 exhibits a key fingerprint resonance at 220.5 ppm, which corresponds to the ipso-carbon, as also confirmed by our relativistic DFT calculations of the NMR chemical shifts (cf.…”

Silver(I) acetylides stabilized by η2-alkynes: Synthesis, reaction chemistry and solid state structures

“…As compared with the free organometallic p-tweezer [Ti](C"CR 1 ) 2 , [5,8] the m C"C absorptions in 6-10 are shifted to lower frequencies as it is generally observed for the g 2 -coordination of alkynes to ML n fragments (ML n = transition metal fragment) in which the alkynes act as 2-electron donor ligands [5,9]. The obtained IR-spectroscopic data for 6-10 demonstrate the influence on the change from a weaker to a stronger r-donor group on the g 1 -bonded acetylide ligands at silver(I), which finally leads to a carbon-carbon triple bond weakening of the g 2 -C"C units.…”

“…Polymeric 14 can be understood as novel lithium salt of a silver(I) bis(acetylide), being formally composed of the anionic [Ag(C"CSiMe 3 ) 2 ] À and cationic [Li(OEt 2 )] + fragments. So far, two structurally closely related polymeric complexes have been described, setup by anionic [Ag(C"CR) 2 ] À (R = SiMe 3 (15), Ph (16) [9], although the difference between the Li-C a and Li-C b bond lengths is very remarkable. In this context it is interesting to refer to [((Me 3 Si) 2 HC) 2 Al(C"CSiMe 3 ) 2 (l-Li)] [9] with an unsolvated lithium ion capped by two acetylide ligands of which the two Li-C distances are different (Li-C a = 2.217(5) Å, Li-C b = 2.425(6) Å).…”

High-valent transition metal corrolazines

“…Strengthening of the Co-C bond through p-back-bonding would be accompanied by a concomitant decrease in C"C bond strength because of electron density placed in the acetylide p * orbital. This in turn would be manifested by an increase in the acetylide bond length, but when comparing C"C in 6 to the average of known MC"CR bond lengths (1.194 (7) vs. 1.201(16) Å ) it is clear that this is not the case [69,73]. A decrease in acetylide bond strength would also be observed by a reduction in the vibrational stretching frequency, however when comparing m(C"C) for 6 (2062 cm À1 ) with triphenylsilylacetylene (2036 cm À1 ) [74] or Co(DO)(DOH)-pn(CCSiMe 3 )(I) (2040 cm À1 ), the opposite trend is observed.…”