Vibrational spectra, molecular structure and rotational isomerism in “staircase” carbonyl complexes of transition metals

Synthesis and structures of the η5-C5H5Cl(CO)2W-η1,η5-(PPh2)C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)3 and MeSi[C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)2PPh3]3 complexes

“…Structurally similar dinuclear complexes with the bridging (PPh 2 )C 5 H 4 ligand and the Mn-Ti or W-Fe combinations have been synthesized earlier. 2, 3 In the previous publication, 4 we have demonstrated that the triphenylphosphine analog of complex 1, η 5 C 5 H 5 (CO) 2 Fe η 1 ,η 5 C 5 H 4 Mn(CO) 2 PPh 3 (5), is also metallated with n butyllithium (THF, -78°C) at the η 5 C 5 H 5 ring. In the present study, we synthesized the propeller like hexanuclear complex MeSi[C 5 H 4 (CO) 2 Fe η 1 ,η 5 C 5 H 4 Mn(CO) 2 PPh 3 ] 3 (6) by the reaction of the lithium derivative of complex 5 with MeSiCl 3 (in a ratio of 3 : 1) (Scheme 3).…”

Binuclear ladder-type complexes as building blocks for the synthesis of novel polynuclear systems

“…Electronic effect of electron donating Cр(CO) n M groups (M = Fe, n = 2; M = Mo, W, n = 3), as well as electron withdrawing M(CO) 3 groups (M = Mn or Cr) is transmitted through the bridging η 1 ,η 5 cyclopentadienyl or η 1 ,η 6 phenyl ligands, being reflected in alteration of vibrational fre quencies of carbonyl groups compared to the mono or dinuclear precursor complexes. 26, 27 The analysis of ν(CO) frequency in binuclear ladder complexes 1 (Fe-Fe), 6 (Fe-Mn), and 24 (Fe-Cr) has shown that Cp(CO) 2 Fe group (a strong electron donor) transfers its electronic effect through η 1 ,η 5 or η 1 ,η 6 bridg ing cyclopentadienyl or phenyl ligands, respectively, resulting in a substantial lowering of ν(CO) frequencies of carbonyl groups attached to Fe, Mn, or Cr atoms relative to the corresponding mononuclear complexes Cp(CO) 2 FeR (R = Alk or Ar), CpMn(CO) 3 or C 6 H 6 Cr (CO) 3 . The electron withdrawing C 5 H 4 (CO) 2 FeR, C 5 H 4 Mn(CO) 3 or C 6 H 5 Cr(CO) 3 groups in their turn enhance stretching frequencies of the carbonyls at Fe atom con siderably compared to the values found in mononuclear complexes Cp(CO) 2 FeR.…”

“…It turned out, however, that under metallation of this complex followed by treatment with electrophilic agent, migration of phenyl ligand coordinated with Cr(CO) 3 from iron atom on cyclopentadienyl ring is very facile. In particular, treatment of the lithiated derivatives of 24 (n BuLi, THF, -78 °C) with PhCH 2 Cl, as well as interaction of the lithiated derivative of η 5 C 5 H 5 (CO) 2 Fe η 1 ,η 6 (C 6 H 4 p Me)Cr(CO) 3 (25) with dimethyl sulfate (Me 2 SO 4 ) resulted in isolation of binuclear complexes PhCH 2 (CO) 2 Fe η 5 ,η 6 (C 5 H 4 -C 6 H 5 )Cr(CO) 3 (26) or Me(CO) 2 Fe η 5 ,η 6 (C 5 H 4 -C 6 H 4 p Me)Cr(CO) 3 (27), respectively (Scheme 10). 23,24 Thus, binuclear com plex 24 cannot be used as a precursor for a trinuclear ladder structure.…”

“…Noticeably, the ν(CO) frequen cies at Fe atom are shifted nearly equally for C 5 H 4 (CO) 2 Fe and C 5 H 4 Mn(CO) 3 groups, indicating their nearly equal electron withdrawing abilities. 26, 27 In a trinuclear Fe-Fe-Mn ladder complex 10 com posed of three metal carbonyl moities, the "top step" ν(CO) frequencies (that is, belonging to the carbonyl attached to Fe atom) are under electron withdrawing influence of two metal carbonyl moities that causes their blue shift with respect to positions in binuclear complex 1. The "bottom step" in 10 is in its turn affected by two electron donating groups, hence ν(CO) frequencies at Mn atom are down shifted from ν(CO) of CpMn(CO) 3 moiety and differ only slightly from ν(CO) at Mn in a binuclear counterpart 6.…”