Synthesis and Coordination Chemistry of an Enantiomerically Pure Pentadienyl Ligand

Abstract

The coordination chemistry of the enantiomerically pure dimethylnopadienyl ligand (Pdl*) with early to late transition metals is presented. Dimethylnopadiene is prepared by a Wittig reaction from (1R)-(−)-myrtenal, which is readily available from the chiral pool. Deprotonation of dimethylnopadiene with a Schlosser base gives K­(Pdl*), which is a good starting material for the preparation of the early- to late-transition-metal open metallocenes [M­(η5-Pdl*)2] (M = Ti, V, Cr, Fe) and mono­(pentadienyl) complexes [(η5-Cp′)­Fe­(η5-Pdl*)] (Cp′ = 1,2,4-(Me3C)3C5H2), [(η7-C7H7)­Zr­(η5-Pdl*)], and [(η4-COD)­Ir­(η5-Pdl*)]. These complexes have been fully characterized by several spectroscopic techniques, elemental analysis, and X-ray crystallography. In all of these cases the Pdl* ligand exhibits excellent face selectivity upon metal coordination, because it coordinates exclusively from the sterically less hindered site of the bicyclic ligand framework. Within the series of open metallocenes [M­(η5-Pdl*)2] (M = Ti, V, Cr, Fe) the open ferrocene is the least thermally stable molecule and degrades to iron metal in solution. This instability is attributed to the severe steric demand of this ligand system in combination with the relatively small Fe2+ center.

Teaching Ferrocenium How to Relax: A Systematic Study on Spin–Lattice Relaxation Processes in tert‐Butyl‐Substituted Ferrocenium Derivatives

“…[9h] and (half‐)open ferrocene derivatives. [17a], In this context, we observed peculiarly slow paramagnetic relaxation, attributed to spin–spin and spin–lattice relaxation processes, for ferrocenium derivatives bearing four, five, or six tert ‐butyl substituents. This finding serves as the starting point for the systematic study described in this contribution, in which we discuss the influence of tert ‐butyl substituents and the counteranions ([BF 4 ] – , [SbF 6 ] – , and [PF 6 ] – ) on the observed spin–spin and spin–lattice relaxation processes.…”

Enantiomerically Pure Constrained Geometry Complexes of the Rare‐Earth Metals Featuring a Dianionic N‐Donor Functionalised Pentadienyl Ligand: Synthesis and Characterisation

“…LnCl 3 (Ln=La, Nd, Dy, Ho) were dried in THF using thionyl chloride to form the corresponding THF adducts, and the content of coordinated THF was determined by elemental analysis. [LaI 3 (thf) 4 ], [30] the bis(alkyl) magnesium compounds [Mg(CH 2 CMe 3 ) 2 ] and [Mg(CH 2 CMe 2 Ph)], [31] [Kpdl*] [8, 10a, b, 32] and ClSiMe 2 NH t Bu [33] were synthesised according to literature procedures. Commercially purchased chemicals were used as received if not otherwise stated.…”

Preparation of enantiomerically pure open calcocene and strontocene complexes and their application in ring opening polymerizations of rac-lactide

“…[35][36][37][38]40 Because of the predominantly ionic bonding in these complexes, the various arrangements are probably enforced by the minimization of inter-ligand repulsions. The coordinated THF molecule resides in the usual position at the open edge of the two pdl* ligands.…”

“…[6][7][8][9][10] There are only scattered reports of pdl complexes acting as catalysts in polymerization processes. [35][36][37][38]40 In the course of these investigations we also set out to close currently existing gaps in the periodic table, to prepare pentadienyl complexes of metals such as the heavier alkaline earths, (Ca, Sr and Ba) 37 that are currently less well explored, and to establish new reactivity patterns. [35][36][37][38]40 In the course of these investigations we also set out to close currently existing gaps in the periodic table, to prepare pentadienyl complexes of metals such as the heavier alkaline earths, (Ca, Sr and Ba) 37 that are currently less well explored, and to establish new reactivity patterns.…”

“…Since the discovery of ferrocene, Cp 2 Fe, organometallic chemistry has been dominated by the cyclopentadienyl (Cp) ligand; a large number of cyclopentadienyl complexes with tailored steric and electronic properties have been developed [1][2][3][4][5] for various applications ranging from material science and small molecule activation to (enantioselective) catalysis. In contrast, the chemistry of the "open" analogues, the pentadienyl ( pdl) ligands, and their corresponding metal complexes has received significantly less attention and the investigations have mainly focused on d-transition metals, [6][7][8][9][10] whereas complexes of the rare earth, [11][12][13][14][15][16][17][18][19][20][21] actinide [21][22][23][24][25] and main group metals [26][27][28][29][30][31][32][33][34][35][36][37][38] have been surprisingly scarce. The diverging developments of these ligand types is surprising, considering that Cp and pdl ligands are indeed related, but pdl derivatives can also adopt different hapticities (Chart 1) and exhibit in its η 5 -U coordination better π-donor and δ-acceptor capabilities, which allow the stabilization of low oxidation states such as Hf(II) and Zr(II).…”