Synthesis and structural characterization of a Meerwein-Ponndorf-Verley/Oppenauer redox intermediate at a tantalum(V) center

Journal Article · Sun Dec 31 23:00:00 EST 1989 · Organometallics; (USA)

DOI:https://doi.org/10.1021/om00115a039· OSTI ID:6661455

Strickler, J R; Bruck, M A; Wexler, P A; Wigley, D E ^[1]

---

1. Univ. of Arizona, Tucson (USA)

The alkyne adducts (DIPP){sub 3}Ta(PhC{triple bond}CPh) (1) and (DIPP){sub 3}Ta(Me{sub 3}SiC{triple bond}CMe) (2, DIPP = 2,6-diisopropylphenoxide) are precursors to the metallacyclic products (DIPP){sub 3}Ta(CPh=CPhCPh(Me)O) (3) and (DIPP){sub 3}Ta(C(SiMe{sub 3})=CMeCPh{sub 2}O) (4) from their reactions with 1 equiv of acetophenone and benzophenone, respectively. (DIPP){sub 3}Ta(PhC{triple bond}CPh) (1) also reacts with 1 equiv of benzaldehyde to form the related metallacyclic compound (DIPP){sub 3}Ta(CPh=CPhCH(Ph)O) (5) in high yield. Excess benzaldehyde reacts with 1 and 2 to form the benzyl alkoxide complexes (DIPP){sub 3}(PhCH{sub 2}O)Ta({eta}{sup 2}-CR=CR{prime}CPh=O) (6, R = R{prime} = Ph; 7, R = Me{sub 3}Si, R{prime} = Me) with a dative bonding interaction between the ring oxygen and the tantalum(V) center. Deuterium-labeling experiments and reactivity studies of this reaction have implicated the oxophilic complex 5 as an intermediate that is capable of transferring a hydride to a weakly coordinated (probably {eta}{sup 1}, O-bound), second molecule of an aldehyde or ketone. Thus, (DIPP){sub 3}(PhCH{sub 2}O)Ta({eta}{sup 2}-CPh=CPhCPh=O) (6), (DIPP){sub 3}(CH{sub 3}CH{sub 2}O)Ta({eta}{sup 2}-CPh=CPhCPh=O) (8), and (DIPP){sub 3}(CH{sub 3}CH{sub 2}(CH{sub 3})CHO)Ta({eta}{sup 2}-CPh=CPhCPh=O) (9) are formed from the reaction of 5 with benzaldehyde, acetaldehyde, and 2-butanone, respectively. The hydride-transfer step of this reaction is equivalent to the Meerwein-Ponndorf-Verley/Oppenauer reactions in which a secondary alkoxide ligand transfers a hydride to the carbonyl of a coordinated aldehyde or ketone. Support that the reaction 5 {yields} 6 proceeds through an {eta}{sup 1}-benzaldehyde intermediate is provided in the isolation of (DIPP){sub 3}({eta}{sup 1}-EtCN)Ta(CPh=CPhCH(Ph)O) (11) from the reaction of (DIPP){sub 3}Ta(CPh=CPhCH(Ph)O) (5) with propionitrile.

• OSTI ID: 6661455
• Journal Information: Organometallics; (USA), Journal Name: Organometallics; (USA) Vol. 9:1; ISSN 0276-7333; ISSN ORGND
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400200* -- Inorganic
Organic
& Physical Chemistry
ALKYNES
CHEMICAL REACTIONS
COMPLEXES
CRYSTAL STRUCTURE
DATA
DATA ANALYSIS
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
REDOX REACTIONS
SYNTHESIS
TANTALUM COMPLEXES
TRANSITION ELEMENT COMPLEXES