Synthesis and Reactivity of Ortho-Mercuriated and Ortho-Palladated Arylacetals and Cyclic and Acyclic Aryldithioacetals. New Examples of the Rearrangement of Acyclic Dithioacetal Aryl- to Dithioether Alkyl-Palladium Complexes

The arylmercurial [Hg{C 6 H 3 (CHO) 2 -2,5}Cl] ( 1 ) reacts with CH(OMe) 3 or HS(CH 2 ) 2 SH to give [Hg{C 6 H 3 {CH(OMe) 2 } 2 -2,5}Cl] ( 2 ) or [Hg(Ar a )Cl] [Ar a = C 6 H 3 {CH(SCH 2 CH 2 S)} 2 -2,5 ( 3a )], respectively. The mercurial 2 or 3a reacts with (NMe 4 ) 2 [Pd 2 Cl 6 ] and 2,2‘-bipyridine (bpy) or with trans -[PdCl 2 (PPh 3 ) 2 ] to give the aryl-palladium complex [Pd{C 6 H 3 {CH(OMe) 2 } 2 -2,5}Cl(bpy)] ( 4 ) or [Pd(κ 2 - C,S -Ar a )Cl(PPh 3 )] ( 5a* ), respectively. The reaction of 1 with NaI 3 renders IC 6 H 3 (CHO) 2 -2,5 ( 6 ), which reacts with HS(CH 2 ) 2 SH to give IAr a ( 7a ). Similarly, IC 6 H(OMe) 3 -2,3,4-(CHO)-6 ( 8 ) reacts with HS(CH 2 ) 2 SH or ToSH (To = C 6 H 4 Me-4) to give the corresponding dithioacetals IAr b [Ar b = C 6 H(OMe) 3 -2,3,4-{CH(SCH 2 CH 2 S)}-6 ( 7b )] or IC 6 H(OMe) 3 -2,3,4-CH(STo) 2 -6 ( 9 ). The iodoarene 7a or 7b adds oxidatively to “Pd(dba) 2 ” (dba = dibenzylideneacetone) to give [Pd(κ 2 - C,S -Ar)(μ-I)] 2 [Ar = Ar a ( 10a ), Ar b ( 10b )], which, in turn, reacts (i) with 1 equiv of PPh 3 to give [Pd(κ 2 - C,S -Ar)I(PPh 3 )] [Ar = Ar a ( 5a ), Ar b ( 5b )], (ii) with Tl(TfO) (TfO = CF 3 SO 3 ) and PPh 3 (1:2:4 molar ratio) to give [Pd(κ 2 - C,S -Ar b )(PPh 3 ) 2 ]TfO ( 11b ), or (iii) with 1 equiv of Tl(TfO) and bpy (1:2:2 molar ratio) to give [Pd(κ 2 - C,S -Ar b )(bpy)]TfO ( 11b* ). Complexes 10 react with 1 equiv of isonitriles to give, after a short period of reaction, the complexes [Pd(κ 2 - C,S -Ar)I(CNR)] [Ar = Ar a, R = Xy = 2,6-dimethylphenyl ( 12a ), t Bu ( 12a ‘); Ar = Ar b, R = t Bu ( 12b ‘)]. The iminoacyl complexes [Pd( κ 2 - C,S -Im)(μ-I)] 2 [Im = Im a ( 13a ), Im b ( 13b )] can be obtained by stirring a solution of 12a for 5 days to give 13a or by reacting 10b with XyNC in 1:1 molar ratio during 22 h to give 13b . Complexes 10 react with 2 equiv of isonitriles to give the iminoacyl complexes [Pd(κ 2 - C,S -Im)I(CNR)] [Im = C( NR)C 6 H 3 {CH(SCH 2 CH 2 S)} 2 -2,5, R = Xy, Im = Im a ( 14a ), R = t Bu, Im = Im a ‘ ( 14a ‘); Im = C( NR)C 6 H(OMe) 3 -2,3,4-(SCH 2 CH 2 S)-6, R = Xy, Im = Im b ( 14b ), R = t Bu, Im = Im b ‘ ( 14b ‘)]. Complexes 14a, b react with 10a, b in 2:1 molar ratio to give 13a, b . Complexes 10a, b react with XyNC and Tl(TfO) (1:4:1) to give the dimeric cations [Pd{( κ 2 - C,S -Im)(CNXy)} 2 (μ-I)]TfO [R = Xy, Im = Im a ( 15a ), Im b ( 15b )]. The compound [Pd{ κ 2 - C,S -Ar c }(μ-I)] 2 ( 16 ) reacts (i) with PPh 3 and Tl(TfO) in 1:4:2 molar ratio to give [Pd II ( κ 2 - C,S -Ar c )(PPh 3 ) 2 ]TfO ↔ [Pd 0 {η 2 -κ 3 - C,S,S - S (To) C HC 6 H(STo)-2-(OMe) 3 -3,4,5}(PPh 3 ) 2 ]TfO ( 17 ), (ii) with isonitriles in 1:2 or 1:4 molar ratio yielding complexes [Pd( κ 2 - C,S -Ar c )I(CNR)] [R = Xy ( 18 ), R = t Bu ( 18 ‘)] or trans -[Pd( κ 1 -C -Ar c )I(CNR) 2 ] [R = Xy ( 19 ), R = t Bu ( 19 ‘)], respectively, and (iii) with PPh 3 in 1:2 molar ratio yielding [Pd(κ 2 - C,S -Ar c )I(PPh 3 )] ( 20 ). The iodoarene 9 reacts with Pd(dba) 2 (i) and PPh 3 (1:1:1 molar ratio) to give [Pd{ κ 2 - C,S -Ar c )I(PPh 3 )] [Ar c = CH(STo)C 6 H(STo)-2- (OMe) 3 -3,4,5 ( 20 )] and (ii) PPh 3 and Tl(TfO) (1:1:2:1 molar ratio) to give 17 . The crystal and molecular structures of 4, 5a*, 14a, and 14b have been determined by X-ray diffraction studies.