Diplatinum(III) Complexes with Four Bridging 1-Methylcytosinato Nucleobases Derived from a Mononucleartrans-(NH₃)₂Pt^IIComplex and Cu^II

Abstract

A heteronuclear complex of composition trans-[(NH(3))(2)Pt(N4-1-MeC(-)-N3)(2)Cu(H(2)O)(2)](ClO(4))(2) (1a), with 1-MeC(-) = 1-methylcytosinate, has been prepared and characterized by X-ray crystallography. 1a (Cu,Pt) is a linkage isomer of a previously described compound with the two metals inverted (Pt,Cu). The intermetallic distances are significantly different in the two types of compounds, 2.6109(9) A in 1a, yet 2.49-2.56 A in several forms of the linkage isomer. When heated in water in the presence of air, 1a is converted in low yield into diplatinum(III) compounds [(H(3)N)Pt(1-MeC(-)-N3,N4)(4)Pt(NH(3))](2+) (2a) and [(H(2)O)Pt(1-MeC(-)-N3,N4)(4)Pt(NH(3))](2+) (2b), which were crystallized as ClO(4)(-) salts. In a modified procedure a third representative of this group of diplatinum(III) compounds, [(O(2)N)Pt(1-MeC(-)-N3,N4)(4)Pt](+) (2c) was isolated. All three compounds contain the four bridging 1-MeC ligands in a head,tail,head,tail arrangement with Pt-Pt distances (2.4516(7)-2.4976(9) A) that are the shortest ones among diplatinum(III) compounds containing nucleobases.

Diplatinum(III) [Cl2(μ2-amidinate)4] compound derived from air oxidation of mononuclear cis-[PtII(NH3)2(amidine-κ1)2]2+ complex

“…[22]. The value of the NCN angle (120.9(3)°) supports the sp 2 character of the central carbon of the amidinate ligand; this angle is smaller than those in [Pt 2 Cl 2 (DPhF) 4 ] (126.1 and 126.2(9)°) [21].…”

“…Among described Pt III species , di-and polynuclear complexes [2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] bearing the homo Pt-Pt and the heteronuclear Pt-M (e.g., M = Au [6], Ru [7], Pd [8]) metal-metal bonds, are the most common. In the vast majority of cases, the metal-metal bond in these species is stabilized by O,O-(phosphates [19], sulphates [2], carboxylates [11,12,18]) O,N-(amidates [2,9,10,[14][15][16][17]23]), P,P-(pyrophosphites [2]), S,N-(pyrimidinthiolates, pyridinethiolates [2,19]), and S,S-(dithiocarboxylates [2]) bridging ligands.…”

“…In the vast majority of cases, the metal-metal bond in these species is stabilized by O,O-(phosphates [19], sulphates [2], carboxylates [11,12,18]) O,N-(amidates [2,9,10,[14][15][16][17]23]), P,P-(pyrophosphites [2]), S,N-(pyrimidinthiolates, pyridinethiolates [2,19]), and S,S-(dithiocarboxylates [2]) bridging ligands. Up to date only few examples of dimeric Pt III species having N,N-bridges (i.e., nucleobases [21] or formamidinates [22]) were reported. These dimers were obtained either directly from the platinum(III) precursor [22] (Scheme 1, a) or via O 2 oxidation of the Pt II Cu II species, where the Cu II center (Scheme 1, b) acts as a mediator for the electron transfer from platinum to molecular oxygen [21].…”

“…Up to date only few examples of dimeric Pt III species having N,N-bridges (i.e., nucleobases [21] or formamidinates [22]) were reported. These dimers were obtained either directly from the platinum(III) precursor [22] (Scheme 1, a) or via O 2 oxidation of the Pt II Cu II species, where the Cu II center (Scheme 1, b) acts as a mediator for the electron transfer from platinum to molecular oxygen [21].…”

“…[24][25][26]), we treated the platinum(II) complexes cis-and trans-[PtCl 2 (RCN) 2 ] with gaseous ammonia and isolated the corresponding cis-and trans-[Pt(NH 3 ) 2 {NH@ C(NH 2 )R} 2 ](Cl) 2 species [27]. One of these Pt II complexes unexpectedly underwent air oxidation without any mediation by other redox active metal centers [21] to achieve a Pt III 2 dimer with N,Nbridges and these results are reported in sections that follow.…”