Secondary Interactions in Phosphane‐Functionalized Group 4 Cycloheptatrienyl–Cyclopentadienyl Sandwich Complexes

Abstract

Twice as reactive: The coordination chemistry of phosphane-functionalized Zr and Hf cycloheptatrienyl-cyclopentadienyl complexes gives rise to unusual secondary interactions associated with the presence of Lewis acidic 16-electron sandwich moieties. These structures can develop weak dative bonds as exemplified by the noncovalent Pd-->Zr interaction in the heterobimetallic {Zr(2)Pd} complex (see picture). Phosphane-functionalized cycloheptatrienyl-cyclopentadienyl Group 4 metal complexes of the type [(eta(7)-C(7)H(7))M(eta(5)-C(5)H(4)PR(2))] (M=Ti (9); M=Zr (10); M=Hf (11); R=Ph (a); R=iPr (b)) have been prepared by the reduction of [(eta(5)-C(5)H(4)PR(2))TiCl(3)] or [(eta(5)-C(5)H(4)PR(2))(2)MCl(2)] (M=Zr, Hf) with magnesium in the presence of cycloheptatriene (C(7)H(8)). In the solid state, the Ti complex 9 a and the complex 11 b are monomeric, whereas 10 a, 10 b, and 11 a form dimers, in which the sandwich units are linked by long Zr-P or Hf-P bonds. Density-functional theory (DFT) calculations indicate that the metal-phosphane interaction is weak, and accordingly, both the Ti complex 9 b and the Zr complex 10 b act as monodentate phosphane ligands upon reaction with [{(cod)RhCl}(2)] (cod=eta(4)-1,5-cyclooctadiene). The X-ray crystal structures of [(cod)Rh(9 b)Cl] (12) and [(cod)Rh(10 b)Cl] (13) reveal that only the latter exhibits a secondary intramolecular Cl-metal interaction. The complex [(10 b)(2)Pd] (14) was obtained by reaction of [(eta(5)-C(5)H(5))Pd(eta(3)-C(3)H(5))] with two equivalents of 10 b. The solid-state structure of 14 reveals a T-shaped Pd(0) center with a long Pd-Zr bond of 2.9709(3) A, which can be interpreted as a weak noncovalent Pd(0)-->Zr(+IV) bond, as indicated by the calculated relaxed force constant of 5.68 N m(-1).

16-Electron cycloheptatrienyl zirconium allyl complexes

“…One viable approach for the synthesis and characterization of novel complexes is the mono-or dilithiation of troticene, [(h 7 -C 7 H 7 )Ti(h 5 -C 5 H 5 )], followed by subsequent reaction with electrophiles, which results in functionalization at either the five-or the seven-membered ring [3] or in strained ansa-complexes [4], respectively. For the heavier analogs of zirconium and hafnium, lithiation has not yet been realized, making any variation of the substituents at the cyclopentadienyl ring rather tedious [5]. An alternative approach has recently provided a versatile and efficient access to various cycloheptatrienyl complexes of zirconium.…”

Cycloheptatrienyl Zirconium Sandwich Complexes with Lewis Basic Phospholyl Ligands (Phosphatrozircenes): Synthesis, Structure, Bonding and Coordination Chemistry

“…For instance, a complex with a weak ZrÀPd interaction was obtained, which was one of only a few earlylate heterobimetallic complexes consisting of neutral complex fragments. [22,23] Although variation and functionalisation of cycloheptatrienyl sandwich complexes have been achieved, these systems again rely on a (substituted) cyclopentadienyl ring as the co-ligand. The only exception is a series of half-open trozircenes, [(h…”

Phosphane‐Functionalized Cycloheptatrienyl–Cyclopentadienyl Titanium Sandwich Complexes: Phosphorus Ligands with an Integrated Reducing Agent for Palladium(0) Catalyst Generation

“…[7,8] Another class of phosphorus ligands derived from the cycloheptatrienyl-cyclopentadienyl (Cht-Cp) titanium sandwich moiety (troticene; 1) was recently introduced by our group, [9] and the troticenyl monophosphanes 2 (R = Ph) and 3 (R = iPr) were initially prepared by the reduction of the corresponding half-sandwich complexes [(h 5 -C 5 H 4 PR 2 )TiCl 3 ] with magnesium in the presence of cycloheptatriene. [10] These phosphanes can be accessed more conveniently by treatment of troticene (1) with n-butyl lithium in the presence of N,N',N',N'',N''-pentamethyldiethylenetriamine (pmdta), and the resulting lithium complex [(h 7 -C 7 H 7 )Ti(h 5 -C 5 H 4 Li·pmdta)] allows selective phosphane functionalization of 1 at the five-membered ring by reaction with chlorophosphanes (ClPR 2 ; Scheme 1). [11] With 2 and 3 in hand, a few rhodium(I), platinum(II), and gold(I) complexes were isolated and structurally characterized, [10,11] and none of them showed any evidence for secondary interactions involving the titanium atom, despite a valence electron count of 16 for the sandwich moiety.…”