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

The metal‐vapor reactions of Co atoms with 1,3‐ t Bu 2 CpH (1a) , 1,3‐ t Bu 2 CpH (1a) , 1,2,4‐ t Bu 3 CpH (1b) and EtMe 4 CpH (1c) are described. With 1a the two mononuclear complexes [(η 5 ‐ t Bu 2 Cp) (η 4 ‐ t Bu 2 ‐1,3‐cyclopentadiene)Co] (2a) and [(η 5 ‐ t Bu 2 Cp) 2 Co] (3a) were isolated, together with the dinuclear cobalt cluster [{(η 5 ‐ t Bu 2 Cp)Co} 2 H 3 ] (4a) and trace amounts of the tetranuclear cluster [{(η 5 ‐ t Bu 2 Cp)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 [{(η 5 ‐ t Bu 3 Cp)Co} 2 H 3 ] (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 Me 5 Cp analog [{(η 5 ‐Me 5 Cp)Co} 2 H 3 ] (4c) . Reaction of an isomeric mixture of Me 4 EtCpH (1c) with Co atoms furnished the mononuclear sandwich [ (η 5 ‐Me 4 EtCp)(η 4 ‐Me 4 Et‐1,3‐ cyclopentadiene)Co] (2b) , the trinuclear hydridocobalt cluster [{(η 5 ‐Me 4 EtCp)Co} 3 H 4 ] (6a) and the tetranuclear hydridocobalt cluster [{(η 5 ‐Me 4 EtCp)Co} 4 H 4 ] (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 [ (η 5 ‐ Cp R )Co(CO) 2 ] (R1,3‐ t Bu 2 , 1,2,4‐ t Bu 3 ) ( 7a and 7b ) as well as [{(η 5 ‐Cp R )CO} 2 (CO) 2 ] ( 8a and 8b ). Reaction of the trinuclear hydridocobalt cluster 6a and its Me 5 Cp analog 6b with AgBF 4 in the presence of PEt 3 yielded the heteronuclear clusters [{η 5 ‐Me 4 CP R )Co} 3 AgP(Et) 3 H 4 ] + [BF 4 ] − (REt, Me) ( 9a and 9b ). 9a was structurally characterized by X‐ray crystallography.