Cationic Group 4 Complexes (M = Ti, Zr, Hf): Modifications and Limitations in the Design of Tridentate Cp,O,P‐Ligand Frameworks Built Directly in the Coordination Sphere of the Metal

Abstract

The reactions of monopentafulvene complexes Ti1, Zr1, and Hf1 with bidentate O,P-ligand precursors L1-L3 to form the corresponding cationic complexes employing an established three-step synthetic protocol [insertion, methylation, activation with B(C 6 F 5 ) 3 ] are investigated. Ligands L1-L3 are designed to have different sized spacers between the carbonyl and diphenylphosphine functional groups. The attempts to react Ti1, Zr1, and Hf1 with acetyldiphenylphosphine (L1) proved to yield undesired products at various steps in the synthetic sequence. When Ti1 is used, Ti2 is formed and diphenylphosphine is released at the same time. Compound Ti2, with the exocyclic double bond, is the formal product of insertion of the smallest ketene (H 2 C=C=O) into the Ti-C exo bond. Starting with [a] 5146 Scheme 2. Targeted cationic group 4 metal complexes of this work. 5147 isolation and purification steps before synthesizing the corresponding complexes. In contrast, our approach allows the preparation of densely functionalized Cp,D,P-tridentate ligands directly in the coordination sphere of the respective group 4 metals in good to excellent yields and under mild reaction conditions. [11,12] As a continuation of our efforts, we herein report on limitations and possibilities to expand and modify the tridentate Cp,O,P-ligand framework of this family of cationic complexes with focus on the ring size of the resulting M,O,P-heterocycles (Scheme 2). Results and Discussion Attempts to Synthesize Cationic Group 4 Metal Complexes with Four-Membered M,O,C,P-UnitsScheme 5. Synthesis of complexes Zr2 and Hf2. 5149Scheme 8. Three-step synthesis of cationic group 4 metal complexes Ti6, Zr6, and Hf6 by reacting monopentafulvene complexes Ti1, Zr1, and Hf1 with L2, subsequent methylation and final activation with B(C 6 F 5 ) 3 . Synthesis of Hf5:To a solution of complex Hf4 (0.200 g, 0.232 mmol) in 15 mL of tetrahydrofuran was added a methyllith-

To Coordinate or not to Coordinate: The Special Role of Chalcogen Ether Functionalities in the Design of Twofold Functionalized Cyclopentadienyl Ligands [Cp,O,Ch (Ch = S, Se)]

“…As can be gathered from Table , the chemical shifts of 2a – 2c and 3a – 3c are in excellent agreement with the previously reported complexes Ia , Ib and IIa , IIb , which were synthesized by the same reaction sequence, thus being highly characteristic for the whole compound class bearing bidentate Cp,O chelating ligands with a donor functional group in the ligand backbone , , …”

“…The ratios of the diastereoisomers were determined by integration of appropriate signals in the 1 H NMR spectra and lie between 4:1 and 15:1. The formations of diastereoisomers in similar ratios was also observed previously by our group for cationic group 4 complexes with tridentate Cp,O,P or Cp,O,N‐ligand systems , , . The most characteristic NMR spectroscopic data of 2a – 2c and 3a – 3c are summarized in Table and compared with the NMR spectroscopic data of Ia , Ib and IIa , IIb , which feature amine or phosphine moieties instead of the chalcogen ether functional groups.…”

“…Whereas the newly formed bond Ti1–O1 with a bond length of 1.854(2) Å constitutes a typical single bond,, the second newly formed bond C16–C26 with a bond length of 1.630(4) Å is significantly elongated compared to typical C(sp 3 )–C(sp 3 ) single bonds . This elongation of the Cp,O σ,π‐chelating ligand framework is comparable to sterically crowded alkanes, and also characteristic for complexes derived from insertion reactions of carbonyl compounds into the polarized M –C q,exo bond of monopentafulvene complexes , , , . The former carbonyl carbon atom C26 is sp 3 ‐hybridizied as shown by the sum of angles around C26 (e.g.…”

“…Inspired by pioneering work concerning the solvent‐ and catalyst free synthesis of various β‐substituted diphenylphosphino ketones, and β‐amino ketones, which are accessible without any further purification steps starting from methyl vinyl ketone and appropriate secondary amines and phosphines, the analogous synthesis of β‐thio ketones was targeted. The reactions of methyl vinyl ketone with propane‐2‐thiol and benzylthiol resulted in clean conversions (shown by 1 H NMR analysis) to the corresponding 1,4‐addition products L1a and L1b within 16 h of vigorous stirring at room temperature (Scheme ).…”

“…Complexes with a Cp,O,P ligand set were synthesized, and their possible modifications and limitations with regard to this special ligand set were pointed out , . Further studies dealt with the corresponding Cp,N,P and Cp,O,N ligand systems and their respective titanium complexes.…”