Group 6 Carbonyl Complexes of C-Ylidic Cp Ligands

Abstract

The synthesis and the analytical features of group 6 carbonyl complexes of electron-poor mono(imidazolium)-and bis(imidazolium)-substituted Cp ylides are presented. With the neutral ylidic imidazolium Cp and the monocationic 1,3bis(imidazolium) Cp ligand all of the group 6 carbonyl complexes were prepared, while in the case of the 1,2-disubstituted Cp ylide only the chromium Cp complex was accessible. The donor properties of the ligands were elucidated experimentally by means of the CO stretching frequencies of their group 6 metal complexes and theoretically by DFT calculations. Every imidazolium substituent and the planar conjugated π system of the imidazolium moieties annelated to the Cp ring increase the average CO stretching frequencies by about 20 cm −1 . Overall, the donor properties of the C-ylidic Cp ligands are still stronger than those of the benzene ligand. Additionally, the protonation of the Cp ligands was investigated, and the basicity correlates qualitatively with the electron-donor character of the ylidic Cp ligands.

An Ylidic Cp and its Scandium Complexes in Equilibrium

“…21,22 Furthermore, the Cp-like reactivity was confirmed and the donor properties were elucidated. 20,21 The coordination of the ylidic Cp ligand can be achieved either by simple addition to the metal center or by substitution of a neutral or anionic ligand. The latter forms the counterion of the imidazolium moiety.…”

“…A – C − and 1 (Scheme ), are a very interesting class of electron-poor Cp ligands. With at least one cationic substituent directly attached to the Cp moiety, the donor strength is reduced in comparison to unsubstituted Cp. , This can lead to stability problems in the presence of coordinating solvents. In the past, we introduced several C -ylidic Cp ligands and used imidazolium moieties to stabilize the cationic charge attached to the Cp: for example, in ligand 1 . , Furthermore, the Cp-like reactivity was confirmed and the donor properties were elucidated. , The coordination of the ylidic Cp ligand can be achieved either by simple addition to the metal center or by substitution of a neutral or anionic ligand.…”

“…With at least one cationic substituent directly attached to the Cp moiety, the donor strength is reduced in comparison to unsubstituted Cp. 20,21 This can lead to stability problems in the presence of coordinating solvents. In the past, we introduced several C-ylidic Cp ligands and used imidazolium moieties to stabilize the cationic charge attached to the Cp: for example, in ligand 1.…”

Assessing the donor ability of boratabenzene and 9-borataphenanthrene anions through metal complexes with carbonyl ligands

“…11 B NMR (128 MHz, CD 3 CN): δ 27.0. FT-IR (cm −1 (ranked intensity)): 2885 (13), 1881 (3), 1793( 4) 1766 (1), 1453 (14), 1351 (9), 1308 (15), 1241 (10), 1095 (2), 955 (6), 888 (11), 834 (5), 694 (8), 645 (7), 543 (12). High-resolution mass spectrometry (HRMS) electrospray ionization (ESI): calculated for C 21 H 26 BCrO 3 Si [M] − , 417.1149; found, 417.1140.…”

“…Yield: 103 mg (48% ), 147.95, 138.87, 136.86, 135.96, 132.16, 129.16, 129.09, 128.78, 127.62, 127.10, 125.50, 123.67, 123.22, 122.94, 122.22, 121.39, 114.22, 112.13, 99.47, 70.20, 68.16, 4.96. 11 (10), 1120 (3), 1060 (12), 942 (7), 830 (8), 743 (1), 702 (15), 599 ( 14), 500 (13). High-resolution mass spectrometry (HRMS) electrospray ionization (ESI): calculated for C 25 H 22 BO 3 SiW [M] − , 593.0941; found, 593.0934.…”