The divergent behavior of palladium(0) and platinum(0) is revealed in the reactivity of [M(PR 3 ) 2 ] (M ) Pd or Pt; R ) Cy or i Pr) toward pentafluoropyridine and 2,3,5,6tetrafluoropyridine. The palladium complexes react with pentafluoropyridine at 100 °C to yield the fluoride complexes trans-[Pd(F)(4-C 5 NF 4 )(PR 3 ) 2 ]. They do not react with 2,3,5,6tetrafluoropyridine. The reaction of platinum(0) complexes [Pt(PR 3 ) 2 ] with pentafluoropyridine in THF at ambient temperature yields trans-[Pt(R)(4-C 5 NF 4 )(PR 3 )(PFR 2 )] complexes, whereas the reaction of [Pt(PCy 3 ) 2 ] with 2,3,5,6-tetrafluoropyridine results in C-H activation to form cis-[Pt(H)(4-C 5 NF 4 )(PCy 3 ) 2 ]; this complex may be converted to the trans isomer by photolysis. The cis-hydride also forms during the reaction of [Pt(PCy 3 ) 2 ] with C 5 NF 5 in hexane. These reactions also contrast with earlier studies of the reactivity of the same substrates toward {Ni(PEt 3 ) 2 }, which yield [Ni(F)(2-C 5 NF 5 )(PEt 3 ) 2 ] with pentafluoropyridine and [Ni(F)-(2-C 5 NF 4 H)(PEt 3 ) 2 ] with tetrafluoropyridine. Thus palladium has different regioselectivity from nickel and is the least reactive. Platinum is capable of both C-F and C-H activation and is alone in the triad in undergoing rearrangement to the alkyl complex with the fluorophosphine ligand. Mechanisms for the rearrangement are proposed. The platinum dihydride complex trans-[Pt(H) 2 (PR 3 ) 2 ] reacts with pentafluoropyridine at room temperature, yielding a 1:1:and trans-[Pt(R)(4-C 5 NF 4 )(PR 3 )(PFR 2 )]. Crystal structures are reported for trans-[Pd(F)(4-C 5 NF 4 )-(PCy 3 ) 2 ]‚H 2 O‚C 6 H 6 , trans-[Pd(F)(4-C 5 NF 4 )(P i Pr 3 ) 2 ], trans-[Pt(C 6 H 11 )(4-C 5 NF 4 )(PCy 3 )(PFCy 2 )]‚ CH 2 Cl 2 , and cis-[Pt(H)(4-C 5 NF 4 )(PCy 3 ) 2 ]. † Dedicated to Professor Helmut Werner on the occasion of his 70th birthday.
The chloro and azido complexes trans-[PdCl(4-C5NF4)(PiPr3)2] (3) and trans-[Pd(N3)(4-C5NF4)(PiPr3)2] (4) can be prepared by reaction of [PdF(4-C5NF4)(PiPr3)2] (2) with Et3SiCl or MeSiN3, respectively. In contrast, reactions of 2 with Ph3SiH or Me2FSiSiFMe2 give the products of reductive elimination 2,3,5,6-tetrafluoropyridine (5) or 4-(fluorodimethylsilyl)tetrafluoropyridine (6) as well as [Pd(PiPr3)2] (1). In a catalytic experiment, pentafluoropyridine can be converted with Ph3SiH into 5 in 62% yield, when 10% of 2 is employed as catalyst. Treatment of trans-[PdF(4-C5NF4)(PiPr3)2] (2) with Bu3SnCH=CH2 in THF at 50 degrees C results in the formation of [Pd(PiPr3)2] (1) and 4-vinyltetrafluoropyridine (7). Complex 2 is also active as a catalyst towards a Stille cross-coupling reaction of pentafluoropyridine with Bu3SnCH=CH2 to give 4-vinyltetrafluoropyridine (7) with a TON of 6. The molecular structure of the complex 3 has been determined by X-ray crystallography.
Treatment of diphenylmercury with an excess of trimethylgallium at higher temperatures resulted in the formation of dimethyl(phenyl)gallium (1). Similarly, reaction of 1-chloromercurio(4-methylbenzene) and 1-chloromercurio(4-tert-butylbenzene) with an excess of trimethylgallium gave dimethyl(4methylphenyl)gallium (2) and dimethyl(4-tert-butylphenyl)gallium (3), respectively. Treatment of diphenylmercury with an equivalent amount of trimethylgallium resulted in the formation of methyl-(diphenyl)gallium ( 4). The X-ray crystallographic studies of compounds 1, 2, 3, and 4 revealed the presence of trigonal planar coordinate gallium atoms in monomeric molecules, which associate to polymeric strands by additional intermolecular gallium π-aryl contacts, thus leading to an overall trigonal bipyramidal coordination geometry at gallium. Compounds 1-4 are stable in the solid state and in solution. Substituent redistribution reactions take place at higher temperatures and at room temperature in the presence of THF. Compound 1 could also be prepared by the reaction of triphenylgallium with an excess of trimethylgallium at higher temperatures.
Benzene derivatives containing dimethylgallyl substituents in 1,3-( compounds 5 and 6), 1,4-(compound 9), and 1,3,5-position (compound 12) were prepared by reaction of the corresponding chloromercuriobenzenes with an excess of trimethylgallium at higher temperatures. These compounds decompose in solution at room temperature and in the solid state upon mild heating with elimination of trimethylgallium to give oligomeric condensation products of unknown detailed composition. These condensation products can be transformed back into the starting compounds by treatment with an excess of trimethylgallium at higher temperatures. Highly air-sensitive crystals of 5, 6, 9, and 12 suitable for an X-ray analysis are obtained from trimethylgallium as solvent. The X-ray crystallographic studies revealed the presence of higher coordinate gallium atoms, which lead to the formation of strand-or sheet-like polymers. A trigonalbipyramidal coordination sphere is observed for the gallium atoms in 9. A distorted tetrahedral coordination is found for the gallium atoms in 5, 6, and 12. The latter compounds possess asymmetric aryl-dimethylgallyl bridging units.
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