The reaction of the cycloheptatrienyl cyclopentadienyl (Cht-Cp) titanium sandwich complexes [(η 7 -C 7 H 7 )Ti(η 5 -C 5 R 5 )] (R = H, Me) with nBuLi followed by treatment with the chlorophosphanes ClPR′ 2 (R′ = Cy, tBu) afforded the Cht-substituted phosphanes [(η 7 -C 7 H 6 PR′ 2 )Ti(η 5 -C 5 R 5 )] (R = H, Me; R′ = Cy, tBu). Together with their previously reported Cp-substituted analogues [(η 7 -C 7 H 7 )Ti(η 5 -C 5 H 4 PR 2 )] (R = Cy, tBu), these complexes were employed as ancillary phosphane ligands in palladium-catalyzed Suzuki-Miyaura coupling between sterically encumbered aryl bromides and aryl boronic acids. The unusually short reaction times indicated rapid generation of catalytically active Pd 0 species, and the reaction of Pd(OAc) 2 with an excess [a] 5588 of the phosphorus ligands afforded linear bis-phosphane palladium(0) complexes. These reactions gave no indication of phosphane oxide formation, and it is supposed that the Cht-Cp titanium sandwich moiety serves as an integrated reducing agent. Accordingly, the reaction of [(η 7 -C 7 H 7 )Ti(η 5 -C 5 M 5 )] with Pd(OAc) 2 or Ag(OAc) resulted in a three-electron redox reaction with formation of the half-sandwich complex [(η 5 -C 5 Me 5 )-Ti(OAc) 3 ] together with 7,7′-bi-1,3,5-cycloheptatriene (ditropyl) and elemental Pd or Ag metal. On reaction with silver(I) trifluoromethanesulfonate, a four-electron redox process furnished the tropylium titanate complex [C 7 H 7 tant examples and have been well studied as ligands in transition-metal-catalyzed reactions, for example, with palladium [38][39][40] or nickel. [41] Chiral ferrocenyl phosphanes V exhibit another possible substitution pattern of the ferrocene backbone and are useful in various catalytic reactions. [42][43][44][45][46][47][48][49][50] Eur.

A series of well-defined palladium allyl chloride precatalysts was synthesized using previously reported troticenyl phosphane ligands [(η 7 -C 7 H 7 )Ti(η 5 -C 5 H 4 PR 2 )] and [(η 7 -C 7 H 6 PR 2 )Ti(η 5 -C 5 H 5 )] (R = Cy, tBu) as ancillary ligands. The formation of a dimeric μ-chloro-, μ-allyl-bridged Pd I species was observed with the ligand [(η 7 -C 7 H 7 )Ti(η 5 -C 5 H 4 PtBu 2 )], whereas L 2 Pd 0 {L = [(η 7 -C 7 H 6 PtBu 2 )Ti(η 5 -C 5 H 5 )]} was formed in presence of KOtPent. In addition, the catalytic activity of the palladium [a] 2569 Scheme 1. Troticenyl phosphane ligands (top) and Pd 0 complexes with ligand 4 tBu and 5 tBu (bottom). 2570 Figure 4. ORTEP diagrams of 7 tBu 1Me, 7 tBu 2Me, and 7 tBu 1Ph (solvent omitted) with thermal displacement ellipsoids drawn at 50 % probability. Hydrogen atoms are omitted for clarity.

Dilithiation of the sandwich complex η7-cycloheptatrienyl-η5-cyclopentadienyl titanium (troticene) with n-butyllithium in the presence of N,N′,N′,N″,N″-pentamethyldiethylenetriamine (pmdta) and subsequent reaction with chlorodialkylphosphanes (ClPR2) afforded the diphosphanes [(η7-C7H6PR2)­Ti­(η5-C5H4PR2)] (4 R , R = iPr, Cy, tBu). The reactions of the cyclohexyl derivative 4 Cy with transition-metal dichlorides furnished the complexes [(4 Cy )­MCl2] (7 M ), which showed tetrahedral (M = Fe, Co Ni, Zn) and square-planar (M = Pd) coordination spheres. The corresponding platinum complexes trans- and cis-[(4 Cy )­PtCl2] (trans- 7 Pt and cis- 7 Pt ) were isolated from the reactions of 4 Cy with either trans- or cis-[(SEt2)2PtCl2], and trans- 7 Pt slowly converted into the thermodynamically more stable cis- 7 Pt within ca. 17.5 h in dichloromethane solution at room temperature. Chloride abstraction from cis- 7 Pt with potassium tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate (KBArF24) gave the bimetallic chloro-bridged complex [(4 Cy )­Pt­(μ-Cl)]2[BArF24]2 (8) or, in the presence of trimethylphosphane (PMe3), the cationic complex [(4 Cy )­PtCl­(PMe3)]­[BArF24] (9); however, these species did not feature the anticiptated titanium–platinum interactions. An intramolecular redox reaction was observed upon the reaction of 4 Cy with cis-[(MeCN)2PtCl2)], affording the titanium­(IV)–platinum(0) complex 10 with a bridging ketimide (MeCN). Density functional theory (DFT) calculations suggest that this complex might have formed via [{(η5-C5H4PCy2)­TiCl2(η1-C7H6PCy2)}­Pt] (11) with subsequent insertion of acetonitrile into the remaining Ti–C bond between titanium and the seven-membered ring.

Invited for the cover of this issue is the group of Matthias Tamm (pictures of first and last authors above) from the Technische Universität Braunschweig, Germany. The cover image shows the selective construction of allyl palladium complexes containing ancillary phosphane ligands based on [(η7‐C7H7)Ti(η5‐C5H5)] (“troticene”).

The Front Cover shows the building block principle of monophosphane ligands based on the 16‐electron cycloheptatrienyl‐cyclopentadienyl titanium sandwich moiety (troticene). The phosphane substituents can be attached selectively either at the seven‐ or five‐membered ring. With these novel ancillary troticenyl phosphane ligands at hand, molecular catalysts can be individually adjusted for applications in homogeneous catalysis: for example, Buchwald‐Hartwig amination reactions are efficiently catalyzed by palladium allyl complexes containing these ligands. More information can be found in the Full Paper by M. Tamm et al. For more on the story behind the cover research, see the Cover Profile.