104241-72-7Relevant articles and documents
Functionalized isocyanides as ligands. 4. Base-promoted cyclization reactions of free and platinum(II)-coordinated o-(phosphoniomethyl)phenyl isocyanide tetrafluoroborates, o-(BF4-R3P+-CH2)C 6H4NC. Synthesis and spectroscopic characterization of 1- and 2-platinum(II)-substituted indole ...
Michelin, Rino A.,Facchin, Giacomo,Braga, Dario,Sabatino, Piera
, p. 2265 - 2274 (2008/10/08)
Full title: Functionalized isocyanides as ligands. 4. Base-promoted cyclization reactions of free and platinum(II)-coordinated o-(phosphoniomethyl)phenyl isocyanide tetrafluoroborates, o-(BF4-R3P+-CH2)C 6H4NC. Synthesis and spectroscopic characterization of 1- and 2-platinum(II)-substituted indole derivatives and X-ray structure of trans-{(PPh3)2Pt[CN(H)-o-C6H 4C(PMe3)]Cl}BF4·C2H 4Cl2. The chloromethyl substituent of the isocyanide o-(ClCH2)C6H4NC easily reacts in CH2Cl2 with the tertiary phosphines PMe3 and PMe2Ph or in acetone in the presence of excess LiBr with the phosphines PMePh2 and PPh3 to give quantitatively the novel phosphonium-substituted isocyanides o-(X-R3P+-CH2)C6H4NC (X = halide), which are more conveniently converted into their less hygroscopic tetrafluoroborate salts o-(BF4-R3P+-CH2)C6H 4NC (L) (PR3 = PMe3 (L1), PMe2Ph (L2), PMePh2 (L3), PPh3 (L4)). Attack of an appropriate base to the activated methylene group of the R3P+-CH2- substituent produces the highly reactive ylide function R3P+-CH-- which undergoes ring closure with the adjacent isocyano group via intramolecular attack of the ylide carbanion to the electrophilic isocyanide carbon (either free or metal-coordinated), affording an indole derivative. Thus, upon treatment in CH2Cl2 at room temperature with a 10-fold excess of the mild base NEt3, the Pt(II)-coordinated ligands L in cationic complexes of the type trans- and cis-[P2Pt(L)X]BF4 (X = Cl, L = L1-L4, P = PPh3 (1-4); X = CH3, L = L1, P = PMePh2 (5), PMe2Ph (6), PCy3 (7); X = Cl, L = L1, P2 = cis-Ph2PCH=CHPPh2 (8)) undergo cyclization reactions to 2-Pt(II)-substituted indole derivatives of the type trans- and cis-{P2Pt[CN(H)-o-C6H4C(PR 3)]X}BF4 (9-15), with reaction times depending on steric and electronic factors due to the ligand and metal substituents. The structures of the final compounds have been assigned on the basis of analytical, spectroscopic (IR and 1H and 31P NMR), and structural data. The solid-state structure of trans-{(PPh3)2Pt[CN(H)-o-C6H 4C-(PMe3)]Cl}BF4·C2H 4Cl2 (9) has been determined by single-crystal X-ray diffractometry: space group P21/m, a = 10.434 (1) A?, b = 23.465 (2) A?, c = 11.725 (1) A?, β = 112.88 (2)°, Z = 2. The structural model was refined to R = 0.040 (Rw = 0.045) for 3961 independent reflections. The coordination geometry around the Pt(II) atom is square-planar with the carbenoid ligand perpendicular to the plane. The Pt-C (sp2) and Pt-Cl bond lengths are 1.99 (1) and 2.369 (1) A?, respectively. Bond lengths within the indole system, which constitutes the carbenoid ligand, indicate extensive electronic delocalization. As a consequence, β-protonation at the indole ring occurs on treating 9 with HBF4. Reaction of the stronger base NaNH2 in THF at room temperature with the uncoordinated isocyanide L4 affords the 3-(triphenylphosphonio)mdolyl ligand: N(o-C6H4)C(PPh3)C(H), which is found to coordinate to Pt(II) at the N(1) position of the indole ring as in the complexes cis-{(PPh3)2Pt[N(o-C6H4)C(PPh 3)C(H)]Cl}BF4 and trans-(PPh3)Cl2Pt[N(o-C6H 4)C-(PPh3)C(H)].
