Diastereotopic exchange in the square-planar platinum(II) complex, (N,N'-dimethylethylenediamine)bis(guanosine)platinum(II)

Abstract

C6H5)3P]2CuBr, 47814-88-0; (dppe)CuI, 15228-76-9. ( 5 5 ) Brint, P.; Spalding, T. R. Inorg. Nucl. Chem. Lett. 1979, 15, 355. A total of six diastereomeric configurations of the chiral square-planar platinum( 11) complex (N,N'-dimethy1ethylenediamine)-bis(guanosine)platinum(II), [Pt(N,N'-Me,en)(Ci~o),]~+, are detected. Three sets of stereoisomers result from the configuration of the two coordinated ethylenediamine nitrogens, and these are designated RR, SS, and SR. In addition, the ribose moieties of the guanosines break all mirror symmetry in and between the stereoisomers, producing pairs of diastereomers possessing different physical and chemical properties. Rotation about the Pt-guanosine bond, which is rapid at 103 'C on the N M R time scale, causes exchange within each pair of diastereomers producing a sharp, four-line, 'H N M R spectrum in the guanosine H(8) region. A complex set of 'H N M R resonances is observed at -32 'C due to slow exchange in the SR set of diastereomers and in one of the RR or SS sets of diastereomers while the fast-exchange peak from the remaining set of diastereomers is only approaching coalescence. The concentration-dependent activation free energy for exchange between the SR diastereomers is about 65 kJ mol-' while that for the higher energy exchange process between the RR or SS diastereomers is about 55 kJ mol-'.

The First Pure ΛHT Rotamer of a Complex with a cis‐[Metal(nucleotide)2] Unit: A cis‐[Pt(amine)2(nucleotide)2] ΛHT Rotamer with Unique Molecular Structural Features

“…For a head-to-tail (HT) orientation of two guanine units, the D or L chirality is defined according to the handedness of two straight lines, one perpendicular to the coordination plane and passing through platinum and the other connecting the O6 atoms of the two guanines. [50,51] www.chemeurj.org be able to crystallize this elusive conformer by choosing those circumstances known from our work to lead to greater stability of the LHT conformer. For this, we selected the 2 ] complex (Me 4 DAE = N,N,N',N'-tetramethyl-1,2-diaminoethane).…”

X‐ray Structure and Circular Dichroism of Pure Rotamers of Bis[guanosine‐5′‐monophosphate(−1)](N,N,N′,N′‐tetramethylcyclohexyl‐1,2‐diamine)platinum(II) Complexes That HaveR,RandS,SConfigurations at the Asymmetric Diamine

“…[14,15] HT conformers have a head-to-tail orientation of the guanine bases and can have either a D or L chirality depending upon the handedness of two straight lines; one passes through the platinum center perpendicularly to the coordination plane, and the other connects the O6 atoms of the two guanines. [16,17] Furthermore, studies with the related [Pt{(S,R,R,S)-bip}G 2 ] and [Pt{(R,S,S,R)-bip}G 2 ] complexes (BIP = 2,2'-bipiperidine) indicated that a mixture of 25 % DHT, 50 % HH, and 25 % LHT essentially had a CD spectrum that lacked any intensity. However, with time, as the HT form became dominant, the intensity of the spectrum increased.…”

Mono‐ and Bis‐Guanosine Adducts of Platinum Complexes with Carrier Ligands Having In‐Plane Steric Bulk: The Case of 1,10‐Phenanthroline and 2,9‐Dimethyl‐1,10‐phenanthroline

“…[13,14] In principle 1,10-phenanthroline (phen) and, even better, 2,9-Me 2 -1,10-phenanthroline (Me 2 phen, neocuproine) could be used to introduce steric bulk in the coordination plane ( Figure 1). 1,10-Phenanthrolines, differently from other chelating diamines, have a very rigid structure and the lone pairs on the nitrogen atoms are convergent and hence ideally oriented for complexation to a metal centre.…”