Well-Defined Silica-Supported Rare-Earth Silylamides

Abstract

Rare-earth silylamides [Ln{N(SiMe3)2}3] [1a-d, Ln = Y (1a), La (1b), Nd (1c), Sm (1d)] react with partially dehydroxylated silica to generate the singly surface-bonded species [(Si-O)Ln{N(SiMe3)2}2] (2a-d). Trimethylsilylation of silanols occurs during the grafting process, affording in fine a hydroxyl-free surface. Contacting these well-defined surface species with excess triphenylphosphine oxide yields [(Si-O)Ln{N(SiMe3)2}2(OPPh3)] surface adducts 3a-d as the major (80%) species, leaving about 20% of unreacted siloxide bisamido species (20%). In addition to elemental analysis and infrared spectroscopy, solid-state NMR spectroscopy was used to characterize these new materials and proved to be a particularly efficient tool for the study of the paramagnetic Nd- and Sm-containing materials and for providing unambiguous verification of OPPh3 coordination on the rare-earth center. Silica-supported rare-earth amides 2a-d are active catalysts for 1-hexene and styrene hydrosilylation and for phenylacetylene dimerization. When compared to the molecular species 1a-d, grafting of the catalyst induces significant changes in the activity and selectivity of these systems.

A Study of Transition‐Metal Organometallic Complexes Combining 35Cl Solid‐State NMR Spectroscopy and 35Cl NQR Spectroscopy and First‐Principles DFT Calculations

“…[5][6][7][8][9][10][11][12] Numerous 1 H, 13 C and 29 Si magic-angle spinning (MAS) SSNMR studies have been reported to date, and constitute the majority of studies of supported/immobilized catalysts. [13][14][15][16][17][18][19][20] A further possibility is the use of SSNMR spectroscopy to probe the transition-metal atoms of the catalytic species and their precursors; our group has demonstrated that such experiments are facile for the bulk spe-Abstract: A series of transition-metal organometallic complexes with commonly occurring metalÀchlorine bonding motifs were characterized using 35 Cl solid-state NMR (SSNMR) spectroscopy, 35 Cl nuclear quadrupole resonance (NQR) spectroscopy, and firstprinciples density functional theory (DFT) calculations of NMR interaction tensors. Static 35 Cl ultra-wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST-QCPMG pulse sequence.…”

Palladium‐Catalyzed Trimerizations of Terminal Arylalkynes: Synthesis of 1,3‐Diaryl‐2‐arylethynyl‐1,3‐butadienes[1]

“…[10] A h 1 -vinylidene complex is able to exhibit several reaction types due to the high reactivity of the carbene carbon. [11] Applying both the s and p nature of a terminal alkyne, 1,4-disubstituted enynes E-3 [12] and Z-3, [12d,13] and 1,3-disubstituted enynes 6 [13b,14] are formed from the head-to-head and head-to-tail dimerization of alkynes, respectively. [15] Selective formation of adducts E/Z-3 or 6 can be achieved by a suitable choice of reaction conditions and catalysts.…”

Well‐Defined Silica‐Supported Calcium Reagents: Control of Schlenk Equilibrium by Grafting

“…Grafting of 2 onto SiO 2 -700 is expected to follow a similar pattern to grafting of the related lanthanide compounds Ln[NA C H T U N G T R E N N U N G (SiMe 3 ) 2 ] 3 . [14] In the latter case, the monopodal species ( SiO)Ln[NA C H T U N G T R E N N U N G (SiMe 3 ) 2 ] 2 is formed through protonolysis of a Ln-amido bond by a silanol group, and a concomitant side reaction was observed in which some of the silanol groups were silylated by the released (Me 3 Si) 2 NH to give SiOSiMe 3 and NH 3 (via transient Me 3 SiNH 2 ). Thus, a silanol-free surface was obtained in fine.…”