Thiophene metal complexes, calculations

Ab initio MO calculations have been carried out on benzo[. ]thiophene (BT), 2-methylbenzo[/ ]thiophene (2-MeBT), 3-methylbenzo[ ]thiophene (3-MeBT), and a number of organometallic complexes containing these thiophenic moieties in an attempt to understand the usual preference for insertion of metal fragments into the sulfur-carbon(vinyl) bond of BT and the recent observations of insertion into the sulfur-carbon(aryl) bond <19980M3798>. 

Additionally, extensive theoretical calculations on such complexes have provided a very deep understanding of the bonding between thiophenes and metal centers and this knowledge has been very helpful in distinguishing the most reasonable proposals to be envisaged in surface chemistry [21-34], This subject is discussed in detail in Chapter 2. 

Concerning theoretical studies of the T (C=C)-coordination of thiophenes to metals, semi-empirical calculations were carried out by Sanchez-Delgado et al. for the model complex (PH3)2(H)2Rh[Ti (C=C)-BT]) -the PPhj analogue of which is an excellent catalyst for the hydrogenation of BT. These calculations indicate that the bonding between the r 2(C=C)-BT and Rh(III) closely resembles the coordination of simple olefins, and consequently BT is activated mainly through a weakening of the C=C bond attached to the metal this renders it susceptible to the transfer of the... 

Gunnoe has also reported examples of catalytic aromatic alkylation using a ruthenium complex and olefins. With propylene and other terminal olefins, a 1.6 1 preference for anti-Markovnikov addition was seen. The proposed mechanism involved olefin insertion into the metal-aryl bond followed by a metathesis reaction with benzene to give the alkylated aromatic and a new metal-phenyl bond (Equation (26)). DFT calculations supported the proposed non-oxidative addition mechanism. The work was extended to include catalytic alkylation of the a-position of thiophene and furan. With pyrrole, insertion of the coordinated acetonitrile into the a-C-H bond was observed. Gunnoe has also summarized recent developments in aromatic C-H transformations in synthesis using metal catalysts. ... 

The results of Fenske-Hall molecular orbital calculations for transition metal thiophene complexes with the ligand bound in 1)5, T l-S-bound, 1)2,1 4 t 4-S-112 and ring-opened modes have been reported335. Formation of Ti -complexes such as [Cp Ir(Ti4-2,5-diinethylthiophene)]2+ was found to be favoured by the presence of elecron-rich metal centres and also to lead to activation of the ring with respect to a ring-opening reaction via a formal oxidative addition reaction. 

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