Facile Formation and Dissociation Behaviour of C–C Bond Resulted from the Nucleophilic Attack of Carbanions on a Carbonyl Carbon in [Pt(hfac)2]

Seichi Okeya, Masato Hashimoto, Fumiko Nakamura, Yoshiaki Kusuyama, Mako Kobayashi, Ryuichi Arakawa
2000 Chemistry Letters  
Pt(hfac) 2 ] (hfac: hexafluoroacetylacetonate) reacts with MeNH 2 in CH 2 Cl 2 /MeOH to give an -NHMe adduct complex on one of the carbonyl carbons, (MeNH 3 )[Pt(hfac)(hfac-NHMe)] 1 which is a tetrahedral intermediate of a Schiff base complex, [Pt(CF 3 COCHC(NMe)CF 3 ) 2 ] 2. Complex 1 activates H 2 O, MeOH, MeNO 2 or acetone in solution to form the corresponding conjugate base adducts. The C-C bond in -CH 2 NO 2 adduct 6, easily cleaves and generates nitromethane in solution. Metal polyamine
more » ... . Metal polyamine complexes react with ketones to give macrocyclic polyimine complexes. On the contrary the reaction of ketone or ketonate complexes with amines to form imines has been scarecely reported. Though [Pd(β-dik) 2 ] (β-dik = acac, hfac) reacts with an excess quantity of MeNH 2 to afford [Pd(MeNH 2 ) 4 ](β-dik) 2 , [Pt(hfac) 2 ] gives the Schiff base complex 2, under the same reaction conditions. 1 The electronattracting CF 3 groups must enhance the reactivity of a carbonyl carbon in hfac ligand. HfacH reacted with water to form the bis(gem-diol) type compound 1,1,1,5,5,5-hexafluoropentane-2,4-tetraol whose deprotonated tetra-anion bridged to two metal atoms to form a dinuclear Mn(III) complex. 2 Recently we reported the formation and structure of a Pd(II) complex with a new C,N-chelate which was derived from the nucleophilic attack of a hydroxy group in the coordinating monoximes on a carbonyl carbon in a central-carbon-bonded hfac ligand. 3 Primary amines attack the carbonyl carbon in ketones or aldehydes nucleophilically to form imines (Schiff base), but a tetrahedral intermediate with -NHR has never been isolated. We report here the preparation and reactions of the intermediate complex which finally becomes complex 2. To [Pt(hfac) 2 ] in CH 2 Cl 2 was added two equivalents of MeNH 2 in MeOH to immediately afford fine orange crystals of complex 1 in 84% yield. The structure of 1 was deduced to be an -NHMe adduct on one of the carbonyl carbons in [Pt(hfac) 2 ]. 4 This means the tetrahedral intermediate of imines is first stabilized in this metal system. Complex 1 gave -OMe adduct complex 3 immediately upon dissolving in MeOH in situ, 5 but after one day red needles of 2 appeared (28% yield). 6 The final product, 2, must have been formed via a small quantity of 1 equilibrated with metastable 3 in solution. The -OH, -CH 2 COCH 3 and -CH 2 NO 2 adducts, 4-6, were also produced after dissolution of complex 1 in CH 3 CN (non-dried), acetone or MeNO 2 , respectively. 7 These structures were supported by the characteristic four line signal patterns observed in the 19 F NMR spectra and the existence of the parent signal in the negative mode ESI-MS. 8 Red crystals of the -OH adduct, 4, were isolated from the reaction of [Pt(hfac) 2 ] and n-Pr 3 N in wet CH 2 Cl 2 (Figure 1 ). 9 Similar -OH adduct with [Co(hfac)(NN) 2 ] 2+ (NN = ethylenediamines) has been reported. 10 In an acetone solution of complex 1 some short-lived species other than 1 were detected by ESI-MS just after dissolution at low temperature (Figure 2) . But a short time after elevating the temperature, only the signal of complex 5 was observed. Complex 6 was isolated from the MeNO 2 solution of 1 in 75% yield as a red crystal which was X-ray analyzed (Figure 3) . 11 The newly formed C-C bond length (1.56(1) Å) is slightly longer than the normal value. Complex 6 liberated free CH 2 DNO 2 in CD 3 OD and transformed to -OCD 3 adduct, 3. 12 Complex 6 liberated MeNO 2 in CD 3 NO 2 and reproduced [Pt(hfac) 2 ] slowly. Complex 4 also equilibrated with [Pt(hfac) 2 ] in CD 2 Cl 2 . It is well known that various nucleophiles; e.g., OH -, H -, H 2 O, NH 3 , 1130 Chemistry Letters 2000
doi:10.1246/cl.2000.1130 fatcat:vs7w3revwfh57kirnzefzxjggq