2, 4‐Dimethylpenta‐1, 3‐dien‐ und 2, 4‐Dimethylpentadienyl‐Komplexe des Rhodiums und Iridiums

Abstract

Die Komplexe [(η4‐C7H12)RhCl]2 (1) (C7H12 = 2, 4‐Dimethylpenta‐1, 3‐dien) und [(η4‐C7H12)2IrCl] (2) wurden durch Reaktion von [(η2‐C2H4)2RhCl]2 bzw. von [(η2‐Cycloocten)2IrCl]2 mit C7H12 erhalten. Die Umsetzung von 1 oder 2 mit CpTl (Cp = η5‐C5H5) liefert die Verbindungen [CpM(η4‐C7H12)] (3a: M = Rh; 3b: M = Ir). Die Hydridabstraktion am Pentadien‐Liganden von 3a, b mit Ph3CBF4 verläuft in Abhängigkeit vom Solvens unterschiedlich. In Aceton oder THF erhält man ausschließlich die “halboffenen” Metallocenium‐Komplexe [CpM(η5‐C7H11)]BF4 (4a: M = Rh; 4b: M = Ir). In Dichlormethan werden Gemische gebildet, die zusätzlich auch die durch elektrophile Substitution am Cp‐Ring entstandenen Spezies [(η5‐C7H11)M(η5‐C5H4CPh3)]BF4 (5a: M = Rh; 5b: M = Ir) sowie die η3‐2, 4‐Dimethylpentenyl‐Verbindung [(η3‐C7H13)Rh{η5‐C5H3(CPh3)2}]BF4 (6) enthalten. Durch Einwirkung von 2, 4‐Dimethylpentadienylkalium auf 1 bzw. 2 werden die Komplexe [(η4‐C7H12)M(η5‐C7H11)] (7a: M = Rh; 7b: M = Ir) gebildet, die in Lösung dynamisches Verhalten zeigen; Versuche zur Synthese der “offenen” Metallocenium‐Kationen [(η5‐C7H11)2M]+ durch Hydridabstraktion von 7a, b scheiterten jedoch. Die neuen Verbindungen wurden elementaranalytisch und spektroskopisch charakterisiert, 4b und 5a auch durch Röntgenstrukturanalyse.

Synthesis, Structure, and Reactivity of Alkyl-Substituted Half-Sandwich η5-Pentadienyl Complexes of Cobalt

“…The η 5 -pentadienyl complexes reported here exhibit 1 H and 13 C NMR spectroscopic data consistent with previously reported η 5 -pentadienyl complexes of the late transition metals. ,, The central proton resonance on the pentadienyl ligand is consistently furthest downfield (δ 6.31−6.78), with the flanking protons on C2 and C4 consistently further upfield (δ 4.65−6.23). Adjacent alkyl substitution deshields the nearby pentadienyl protons, regardless of position.…”

“…Acyclic η 5 -pentadienyl complexes of cobalt, rhodium, and iridium are reasonably abundant and have been prepared by a range of synthetic strategies. , Nonetheless, only a limited number of pentadienyl substitution patterns have been reported, dominated by the unsubstituted pentadienyl and 2,4-dimethylpentadienyl ligands. Potentially the most general synthetic approach is the coordination and protolytic dehydration of conjugated dienyl alcohols, a method first reported by Petit for the preparation of η 5 -pentadienyl iron complexes and subsequently adapted to the synthesis of η 5 -pentadienyl complexes of rhodium and iridium. − Low- − and high-valent − η 5 -pentadienyl complexes of cobalt have been reported, although Co(III) η 5 -pentadienyl complexes are relatively rare.…”

H2 Activation and Direct Access to Terminal Nitride and cyclo-P3 Complexes by an Acceptor-Free Rhenium(II) β-Diketiminate

“…We did note that a small amount of C was generated in these reaction mixtures, though we cannot confirm whether this was from the reaction of B with H 2 generated in situ or by some other pathway. There are several reports of trityl substitution to Cp ligands of transition-metal complexes, though none of these examples involve subsequent cyclometalation to yield the dianionic tritylcyclopentadienyl ligand found in 2 . − …”

“…These complex and broad signals originate from the orientation selection of anisotropic 31 P hyperfine couplings as well as the overlapping of the ENDOR signals of three 31 P atoms; therefore, the extraction of accurate hyperfine tensors was not attempted. Nevertheless, the hyperfine tensor of A 31 P = [24,12,12] MHz read off from the field-dependent ENDOR spectra gives a iso = 16 MHz and T = 4 MHz, which corresponds to very small 3s spin densities of 0.001 and 3p spin densities of 0.01 on each 31 P atom (see Supporting Information) that add up to only 0.03 total spin density on the cyclo-P 3 ligand. We employed density functional theory (see Supporting Information) to substantiate these findings, and the calculations also indicated a minimal degree of spin density is expected to lie on the cyclo-P 3 ligand in 5 + .…”

Synthesis and Coordination Chemistry of an Enantiomerically Pure Pentadienyl Ligand

“…Attempts to prepare open cobaltocenes [Co­(η 5 -Pdl) 2 ] have been unsuccessful, and instead reduction to Co­(I) has been observed . However, cationic pentadienyl Co­(III) complexes can be stabilized by a (η 5 -C 5 H 5 )Co or (η 5 -C 5 Me 5 )Co fragment. , For the heavier cobalt congener iridium, iridium­(I) heteropentadienyl complexes such as [(η 4 -COD)­Ir­(μ 2 -1-2,5-η-CH 2 CHCHCHSO)] 2 and cationic iridium­(III) pentadienyl complexes such as [(η 5 -C 5 H 5 )­Ir­(η 5 -C 5 H 5 Me 2 -2,4)]­[BF 4 ] have only recently been reported.…”