In:
Zeitschrift für Naturforschung B, Walter de Gruyter GmbH, Vol. 50, No. 11 ( 1995-11-1), p. 1601-1616
Abstract:
In the quest of suitable precursors for the synthesis of Mo(IV) carbonyl complexes the compounds [Mo(CO) 2 (PCy 3 )(′ bu S 4 ′)] (3) and [Mo(CO) 2 (PCy 3 )(′S 4 ′)] (4) [′ bu S 4 ′ 2- = 1,2-bis(2-mercapto-3,5-di-t-butyl-phenylthio)ethane(2-); ′S 4 ′ 2- = 1,2-bis(2-mercaptophenylthio)ethane(2-)] were synthesized via CO substitution from [Mo(CO) 3 (′ bu S 4 ′)] (13) and [Mo(CO) 3 (′S 4 ′)](14). 4 was characterized by X -ray structure analysis and exhibits, due to the sterically demanding PCy 3 , a strongly compressed [Mo(′S 4 ′)] core. Intramolecular redox reactions of 3, 4 and, in addition, [Mo(CO) 2 (PMe 3 )(′S 4 ′)] (15) leading to thioether dealkylation via loss of C 2 H 4 from the ′ R S 4 ′ 2- ligands and Mo(II)→ Mo(IV) oxidation yielded the Mo(IV) complexes [Mo(CO)(PCy 3 )(′ bu S 2 ′) 2 ] (6), [Mo(CO)-(PCy 3 )(′S 2 ′) 2 ] (7) and [Mo(CO)(PMe 3 )(′S 2 ′) 2 ] (8) [′ bu S 2 ′) 2 ]= 3,5-di-t-butyl-1,2-benzenedithiolate(2-), ′S 2 ′ 2- = 1,2-benzenedithiolate(2-)]. Depending on the nature of the phosphines and the R substituents of the ′ R S 4 ′ 2- ligands, the syntheses required very specific reaction conditions ranging from thermolysis in vacuo to heating in boiling THF. For instance, [Mo(CO) 2 (PCy 3 )(′S 4 ′)] (4) decomposes in CH 2 Cl 2 solution even at ambient temperature yielding the binuclear Mo(II) complex [Mo(CO)(μ-′S 4 ′)] 2 (10), which was characterized by an X-ray structure determination. Thermolysis of 4 in vacuo at 80 °C , however, results in the formation of the Mo(IV) complex 7. By optimizing the reaction conditions preparative amounts of the prototype [Mo(CO) 2 (′ bu S 2 ′) 2 ] (1) have now also become accessible. These findings can be rationalized in part on the basis of results obtained from cyclic voltammetry. The redox potentials of the Mo(IV) complexes are drastically shifted by about -0.5 V per substitution of CO by PR 3 , and the substitution of ′S 2 ′ 2- by ′ bu S 2 ′ 2- ligands causes a negative shift in the range from 0.03 V to 0.18 V. The results of IR spectroscopical m onitoring the substitution of CO by PMe 3 in [Mo(CO)(PMe 3 )(′ R S 2 ′) 2 ] yielding [Mo(PMe 3 ) 2 (′ R S 2 ′) 2 ] suggested an associative substitution mechanism via the intermediate [Mo(CO)(PMe 3 ) 2 (′ R S 2 ′) 2 ]. The formation of [Mo(CO)-(PMe 3 )(′ bu S 2 ′) 2 ] (12) from [Mo(PMe 3 ) 2 (′ bu S 2 ′) 2 ] (9) and CO under standard conditions further shows that the direct coordination of CO to Mo(IV ) centers is also possible if these centers are surrounded by thiolate donors. The results are discussed with respect to the reactivity of the Mo centers of the FeMo cofactors in nitrogenases.
Type of Medium:
Online Resource
ISSN:
1865-7117
,
0932-0776
DOI:
10.1515/znb-1995-1106
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
1995
detail.hit.zdb_id:
2078109-X
detail.hit.zdb_id:
124635-5
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