One bond Pt–P coupling constants 1JPtP of a series of cationic complexes [PtXL(PPh3)2]+ (X = NO3, Cl, Br, I; L = 4-Z-pyridines, Z = electron withdrawing or releasing groups, 4a–k; or X = Cl, L = NH3, PhCH2NH2 and iPrNH2, 5a–c) have been used to establish the trans and cis inﬂuence sequences of X and pyridines. The crystal structure of compound 4f(BF4) with Z = tBu has been resolved. In the pyridine complexes 4a–d (Z = H, variable X), both the trans and cis inﬂuence series of the anionic ligands X decrease along the same sequence I > Br > Cl > NO3, as previously found for [PtX(PPh3)3]+ (X = NO3, Cl, Br, I, 3a–d), however in 4a–d the cis inﬂuence turns out to be more important than the trans. On the contrary, in [PtCl(4-Z-py)(PPh3)2]+ (4b,e–k) the sequence of the trans inﬂuence of the 4-Z-pyridines is opposite to that of the cis, the latter being Z = CN > CHO > Br > PhCO > H > Me > tBu > NH2, i.e. the most basic pyridine gives rise to the lowest cis inﬂuence. This correlation was found to hold also for complexes 5a–c (L = amines). All the observed trends have been fully reproduced by B3LYP/def2-SVP DFT calculations, by looking at the relevant optimized bond lengths of selected complexes of type 3, 4 and 5. Subsequent evaluation of the atomic charges, by resorting to two independent methods, i.e., the Natural Bond Order analysis of the wavefunction and the Bader’s Quantum Theory of Atoms in Molecules, allowed for rationalization of the origin of the cis and trans inﬂuences. The negative charge on the nitrogen atoms of free pyridines becomes more negative upon protonation and even more so when coordinated to the [PtCl(PPh3)2]+ moiety. The least negatively charged nitrogen atom of coordinated pyridines is that of 4-CN-py (the highest cis inﬂuencing pyridine derivative), which gives rise to the lowest positive charge on Pt, conﬁrming the relationship between the lowering of the charge on the metal ion and a high cis inﬂuence. The trans inﬂuence can be described in terms of competition between the charges on the two trans donor atoms. In contrast with the behaviour of pyridines, the positive charge on the phosphorous atom of free PPh3 increases upon coordination to Pt(II), moreover the PPh3 ligands acquire a substantial positive charge, thus efﬁciently delocalising the charge of the cationic complex.
The role of the atomic charges on the ligands and platinum(II) in affecting the cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L = 4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation / L. Rigamonti, M. Rusconi, A. Forni, A. Pasini. - In: DALTON TRANSACTIONS. - ISSN 1477-9226. - 40:39(2011), pp. 10162-10173.
|Titolo:||The role of the atomic charges on the ligands and platinum(II) in affecting the cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L = 4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation|
RIGAMONTI, LUCA (Primo)
RUSCONI, MICHELE (Secondo)
PASINI, ALESSANDRO (Ultimo)
|Parole Chiave:||Platinum ; Phosphine ; Pyridine ; DFT Calculations ; Atomic charges|
|Settore Scientifico Disciplinare:||Settore CHIM/03 - Chimica Generale e Inorganica|
|Data di pubblicazione:||2011|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1039/C1DT10963D|
|Appare nelle tipologie:||01 - Articolo su periodico|