Isolation and Chemistry of Tantalum(V) Compounds Containing Two Resolved 3,3‘-Disubstituted-1,1‘-bi-2,2‘-Naphthoxide Ligands

Abstract

Reaction of dimeric [(Et2N)2Cl2Ta(μ-Cl)2TaCl2(NEt2)2] with (R)-[H2O2C20H10(R)2-3,3‘] (R = SiMe3, SiMe2Ph, SiMePh2, or SiPh3) produces the 3,3‘-dialkyl-1,1‘-bi-2,2‘-naphthoxido complexes (R,R)-[H2NEt2][Ta(O2C20H10{R}2-3,3‘)2Cl2] (R = SiMe3, (R,R)-1; SiMe2Ph, (R,R)-2; SiMePh2, (R,R)-3; SiPh3, (R,R)-4). Structural studies of the SiMe3 derivative (R,R)-1 show a pseudo-octahedral anion with mutually cis chloride ligands. Although NMR studies indicate that the anion of (R,R)-1 is stable in DMSO-d 6, an equilibrium mixture is observed in C6D6 solution with the neutral complex (R,R)-[Ta{O2C20H10(SiMe3)2-3,3‘}2Cl], (R,R)-1a, and [H2NEt2]Cl. The temperature dependence of the equilibrium has been studied. Addition of [nBu4N]Cl to a mixture of (R,R)-1/(R,R)-1a in C6D6 is shown (1H NMR) to shift the equilibrium toward (R,R)-1. Alkylation of (R,R)-1 with Grignard reagents RMgCl results in formation of the five-coordinate (R,R)-[Ta(O2C20H10{SiMe3}2-3,3‘}2R‘] (R‘ = CH2SiMe3, (R,R)-5; CH2Ph, (R,R)-6; c-C5H9, (R,R)-7).

Synthesis of the Tantalum Hydride Complex (R,R)-[Ta(O2C20H10{SiMe3}2-3,3‘)2(H)] and Reactivity with Aldehydes, Ketones, Acetylenes, and Related Substrates: A Reagent for the Asymmetric Hydrogenation of Prochiral Carbonyl Species

“…The phenyl complex ( R , R )-[Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 (Ph)], ( R , R )- 1 , was prepared by the reaction of PhMgCl with ( R , R )-[H 2 NEt 2 ][Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 Cl 2 ] via the method used for the preparation of the alkyl complexes ( R , R )-[Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 (R)] (R = CH 2 SiMe 3 , CH 2 Ph, or c -C 5 H 9 ), as shown in Scheme . The identity of ( R , R )- 1 was confirmed by NMR spectroscopy which indicates the presence of one phenyl group attached to the tantalum metal center.…”

“…All manipulations were carried out using standard Schlenk line, glovebox, and syringe techniques . The compound [H 2 NEt 2 ][Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 Cl 2 ] was prepared according to a previously published procedure . Reagents were purchased from Aldrich and used without further purification.…”

“…Mono- and dihydride complexes of the heavy group 5 metals niobium and tantalum with ancilliary aryloxide ligation have been shown to function as catalysts for the hydrogenation of unsaturated hydrocarbons. − Previous work has focused on hydrogenation reactions using species containing achiral aryl ligands, although ( S )-[Ta(O 2 C 20 H 10 -3,3‘-{SiMe 3 } 2 )(H)(Cl) 2 (PMe 3 ) 2 ], which contains a resolved chiral binaphthoxide ligand, has been recently prepared and has the potential to function as an asymmetric hydrogenation catalyst . Although the binaphthoxide ligand is an important chiral auxiliary in complexes of titanium, substantially fewer examples of related heavy group 5 complexes have been reported. − We have prepared and characterized the salt complex ( R , R )-[H 2 NEt 2 ][Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 Cl 2 ], which serves as a precursor for various organometallic species of the formula ( R , R )-[Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 (R)] (R = CH 2 SiMe 3 , CH 2 Ph, or c -C 5 H 9 ) . We now wish to report the use of ( R , R )-[H 2 NEt 2 ][Ta(O 2 C 20 H 10 {SiMe 3 } 2 -3,3‘) 2 Cl 2 ] for the preparation of a hydride complex that contains two resolved binaphthoxide ligands and serves as a hydrogenation agent for aldehydes, ketones, and acetylenes.…”

Isolation and Chemistry of Aluminum Compounds Containing (S)-3,3‘-Bis(triphenylsilyl)-1,1‘-bi-2,2‘-naphthoxide Ligands

“…Metal dialkylamido compounds have proven extremely useful substrates for the synthesis of the corresponding alkoxides and aryloxides. In fact we have found that there are many synthetic advantages to the use of transition metal dimethylamides for the sunthesis of binaphthoxide derivatives over the use of more traditional halide starting materials . The reaction of the compound [LiAl(NMe 2 ) 4 ] with ( S )- 1 leads to a new mixed metal product containing (as determined by 1 H NMR) both dimethylamido and dimethylamino groups.…”

Novel germanium(ii) binaphthoxide complexes: synthesis and crystal structure of (R,R)-[Ge{OC20H10(OSiMe3)-2′-(SiMe3)2-3,3′}2] and (R)-[Ge{O2C20H10(SiMe2Ph)2-3,3′}{NH3}]; catalytic function of Ge[N(SiMe3)2]2 for the mono-silylation of 3,3′-disubstituted-1,1′-bi-2,2′-naphthols

“…3 We have begun an investigation into the inorganic and organometallic chemistry that can be supported by resolved 3,3Ј-disubstituted-1,1Ј-bi-2,2Ј-naphthol as a ligand with metal complexes of tantalum. 4, 5 We now wish to report the preparation and structure of two novel germanium binaphthoxide complexes, (R,R)-[Ge{OC 20 H 10 (OSiMe 3 )-2Ј-(SiMe 3 ) 2 -3,3Ј} 2 ] (1) and (R)-[Ge{O 2 C 20 H 10 (SiMe 2 Ph) 2 -3,3Ј}{NH 3 }] (2) and the catalytic activity of Ge[N(SiMe 3 ) 2 ] 2 for the selective silylation of one hydroxyl group of (R)-[(HO) 2 C 20 H 10 (R) 2 -3,3Ј] (R = SiMe 3 3; SiMe 2 Ph 4; SiMePh 2 5; SiPh 3 6). 6 The germanium bisamide Ge[N(SiMe 3 ) 2 ] 2 7 reacts with two equivalents of (R)-[(HO) 2 C 20 H 10 (SiMe 3 ) 2 -3,3Ј] (3) over 12 h in benzene to produce complex 1 in 32% overall yield.…”