Irreversible insertion of benzonitrile into platinum(II)-nitrogen bonds of nucleobase complexes. Synthesis and structural characterization of stable azametallacycle compounds.
Deprotonation of 1-methylcytosine (1-MeCy) and 9-methyladenine (9-MeAd) promoted by cis-[L(2)Pt(mu-OH)](2)(NO(3))(2) (L = PPh(3), PMePh(2), (1)/(2)dppe) in PhCN causes the irreversible insertion of a nitrile molecule into the Pt-N4 and Pt-N6 bonds of the cytosinate and adeninate ligands, respectively, to form the stable azametallacycle complexes cis-[L(2)PtNH=C(Ph){1-MeCy(-2H)}]NO(3) (L = PPh(3), 1; PMePh(2), 2; (1)/(2)dppe, 3) and cis-[L(2)PtNH=C(Ph){9-MeAd(-2H)}]NO(3) (L = PPh(3), 4; PMePh(2), 5) containing the deprotonated form of the molecules (Z)-9-N-(1-methyl-2-oxo-2,3-dihydropyrimidin-4(1H)-ylidene)benzimidamide and (Z)-N-(9-methyl-1H-purin-6(9H)-ylidene)benzimidamide. Single-crystal X-ray analyses of 2 and 4 show the metal coordinated to the N3 cytosine site [Pt-N3 = 2.112(7) A] and to the N1 site of adenine [Pt-N1 = 2.116(6) A] and to the nitrogen atom of the inserted benzonitrile [Pt-N2 = 2.043(6) and 2.010(6) A in 2 and 4, respectively], with the exocyclic nucleobase amino nitrogen bound to the carbon atom of the CN group. Complex 2, in solution, undergoes a dynamic process related to a partially restricted rotation around Pt-P bonds, arising from a steric interaction of the oxygen atom of the cytosine with one ring of the phosphine ligands. The reaction of 4 with acetylacetone (Hacac) causes the quantitative protonation of the anionic ligand, affording the acetylacetonate complex cis-[(PPh(3))(2)Pt(acac)]NO(3) and the free benzimidamide NH=C(Ph){9-MeAd(-H)}. In the same experimental conditions, complex 3 reacts with Hacac only partially.
Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padova, Italy.
Diego
D
Montagner
Alfonso
A
Venzo
Ennio
E
Zangrando
Bruno
B
Longato
D000225:Adenine / Q000031:analogs & derivatives / Q000737:chemistry; D001372:Aza Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003596:Cytosine / Q000031:analogs & derivatives / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009570:Nitriles / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*
D001372:Aza Compounds; D009570:Nitriles; C031532:1-methylcytosine; D010984:Platinum; C013115:9-methyladenine; D003596:Cytosine; C014356:benzonitrile; D000225:Adenine; D009584:Nitrogen