Metal Atoms in the Synthesis of Metal Clusters, VIII.On the Reaction of Sterically Demanding Cyclopentadiene Ligands with Cobalt Atoms: Synthesis, Crystal Structure, Spectroscopic Behavior, and Reactivity of Di-, Tri- and Tetranuclear Hydrido Clusters of Cobalt

Abstract

The metal‐vapor reactions of Co atoms with 1,3‐tBu2CpH (1a), 1,3‐tBu2CpH (1a), 1,2,4‐tBu3CpH (1b) and EtMe4CpH (1c) are described. With 1a the two mononuclear complexes [(η5‐tBu2Cp) (η4‐tBu2‐1,3‐cyclopentadiene)Co] (2a) and [(η5‐tBu2Cp)2Co] (3a) were isolated, together with the dinuclear cobalt cluster [{(η5‐tBu2Cp)Co}2H3] (4a) and trace amounts of the tetranuclear cluster [{(η5‐tBu2Cp)CoH}4] (5a). The molecular structures of 3a and 4a were determined by X‐ray diffraction. Reaction of 1b with Co atoms afforded a single product, the dinuclear cluster [{(η5‐tBu3Cp)Co}2H3] (4b), whose molecular structure was determined by single‐crystal X‐ray diffraction. Both, 4a and 4b exhibit extremely short Co‐Co distances [2.244(1) (4a) and 2.242(1) Å (4b)], as found for the Me5Cp analog [{(η5‐Me5Cp)Co}2H3] (4c). Reaction of an isomeric mixture of Me4EtCpH (1c) with Co atoms furnished the mononuclear sandwich [ (η5‐Me4EtCp)(η4‐Me4Et‐1,3‐ cyclopentadiene)Co] (2b), the trinuclear hydridocobalt cluster [{(η5‐Me4EtCp)Co}3H4] (6a) and the tetranuclear hydridocobalt cluster [{(η5‐Me4EtCp)Co}4H4] (5c). The molecular structure of 5c was determined by X‐ray crystallography and revealed a tetrahedral arrangement of the cobalt atoms. The electrochemical behavior of the dinuclear complexes 4a‐4c was studied by cyclic voltammetry. Reversible redox couples were found for all three compounds, with a correlation between the degree of alkyl substitution and their respective cathodic shifts. Compounds 4a and 4b react with CO to yield the mononuclear and dinuclear complexes [ (η5‐ CpR)Co(CO)2] (R1,3‐tBu2, 1,2,4‐tBu3) (7a and 7b) as well as [{(η5‐CpR)CO}2(CO)2] (8a and 8b). Reaction of the trinuclear hydridocobalt cluster 6a and its Me5Cp analog 6b with AgBF4 in the presence of PEt3 yielded the heteronuclear clusters [{η5‐Me4CPR)Co}3AgP(Et)3H4]+[BF4]− (REt, Me) (9a and 9b). 9a was structurally characterized by X‐ray crystallography.

Neutron Diffraction Study of [H4Co4(C5Me4Et)4], a Tetrahedral Metal Cluster Complex with Four Face-Bridging Hydride Ligands

“…The positions of the hydride ligands were not determined in the earlier X-ray structure determination. 3 In the present neutron analysis they appeared as negative peaks in the difference Fourier maps and were found to be on the cluster surfaces at the four face-bridging sites. All the other H atoms in the structure (the 136 hydrogen atoms of the C-H groups) were also unambiguously located in this manner.…”

(μ3-Hydrido)[μ3-2-(trimethylsilyl)ethylidyne-κ3C1:C1:C1]tetrakis[(η5-cyclopentadienyl)cobalt(II)]

“…For other tetranuclear Co clusters with a tetrahedral Co 4 core featuring 3 -bridging hydrido ligands, see: Huttner & Lorenz (1975); Stella et al (1988); Wadepohl & Pritzkow (1993); Schneider et al (1997); Bau et al (2004). [CpCo] 4 clusters with 3 -bridging carbonyl groups are described by Gambarotta et al (1985) and Stella et al (1988).…”

Bis(η5-1,3-di-tert-butylcyclopentadienyl)chromium(II)

“…The compound is isostructural with the iron and cobalt analogues, which are the only other base-free transition metal metallocenes with this ligand that have been structurally characterized (Boese et al, 1993), (Schneider et al, 1997). Table 1 gives selected bond distances and angles for (I); Cg1 and Cg2 are the calculated centroids of the rings C1 -C5 and C6 -C10, respectively.…”