Quantiﬁcation of cis and trans inﬂuences in [PtX(PPh 3 ) 3 ] + complexes. A 31 P NMR study Luca Rigamonti a , Michele Rusconi a , Carlo Manassero b , Mario Manassero b,* , Alessandro Pasini a, ** a Università degli Studi di Milano, Dipartimento di Chimica Inorganica, Metallorganica e Analitica ‘‘Lamberto Malatesta”, via Venezian 21, 20133 Milano, Italy b Università degli Studi di Milano, Dipartimento di Chimica Strutturale e Stereochimica Inorganica, via Venezian 21, 20133 Milano, Italy article info Article history: Received 4 June 2010 Accepted 1 July 2010 Available online 7 July 2010 Keywords: cis inﬂuence trans inﬂuence cis inﬂuence weight trans inﬂuence weight Platinum phosphine complexes abstract In [PtX(PPh 3 ) 3 ] + complexes (X = F, Cl, Br, I, AcO, NO 3 , NO 2 , H, Me) the mutual cis and trans inﬂuences of the PPh 3 groups can be considered constants in the ﬁrst place, therefore the one bond Pt–P coupling con- stants of P (cis) and P (trans) reﬂect the cis and trans inﬂuences of X. The compounds [PtBr(PPh 3 ) 3 ](BF 4 )(2), [PtI(PPh 3 ) 3 ](BF 4 )(3), [Pt(AcO)(PPh 3 ) 3 ](BF 4 )(4), [Pt(NO 3 )(PPh 3 ) 3 ](BF 4 )(5), and the two isomers [Pt(NO 2 - O)(PPh 3 ) 3 ](BF 4 )(6a) and [Pt(NO 2 -N)(PPh 3 ) 3 ](BF 4 )(6b) have been newly synthesised and the crystal struc- tures of 2 and 4CH 2 Cl 2 0.25C 3 H 6 O have been determined. From the 1 J PtP values of all compounds we have deduced the series: I > Br > Cl > NO 3 > ONO > F > AcO > NO 2 > H > Me (cis inﬂuence) and Me > H > NO 2 > A- cO > I > ONO > Br > Cl > F > NO 3 (trans inﬂuence). These sequences are like those obtained for the (neutral) cis- and trans-[PtClX(PPh 3 ) 2 ] derivatives, showing that there is no dependence on the charge of the com- plexes. On the contrary, the weights of both inﬂuences, relative to those of X = Cl, were found to depend on the charge and nature of the complex. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction cis and trans inﬂuences of a ligand X can be deﬁned as the ability of that ligand to weaken the bond between a metal and a ligand L, respectively, cis or trans to X [1–6]. The comprehension of these inﬂuences is therefore important for understanding and rationalis- ing some properties of square planar and octahedral transition me- tal complexes. These include stability, occurrence of geometrical isomers, bond strengths, as well as ligand reactivity (through the link with the cis and trans effects) [1–5]. Because of such importance, these inﬂuences have been the subject of many inves- tigations from their early recognition [6] to the present days [2,3,7–10]. Interestingly, the scope of these inﬂuences has recently been expanded, since they were found to play a role also in main group [11] and lanthanide chemistry [12]. These studies were mostly based on either X-ray crystallogra- phy or spectroscopic (IR and NMR) investigations, although both techniques suffer some limitations. Thus X-ray derived M–L bond lengths may be affected by crystal packing and conformational ef- fects and only few M–L bond stretches can be unambiguously as- signed (M–H, certain M–Cl and few others); CO stretching frequencies have also been used [13]. NMR investigations are usu- ally based on the values of one bond coupling constants, which can be considered an estimate of the M–L bond strength [1,13–19], but this technique can be used only when both M and the donor atom of L are NMR active ( 195 Pt– 31 P, 103 Rh– 31 P, etc.). 2 J MC and 3 J MH have also been employed [1,20]. We have recently been studying cis and trans inﬂuences in Pt(II) bis(triphenylphosphine) complexes. In a ﬁrst paper [21] we have used the one bond Pt–P coupling constants to evaluate the order of cis inﬂuence of some anionic ligands X and Y in a series of trans-[PtXY(PPh 3 ) 2 ] complexes (type A, see Scheme 1). In these compounds the mutual trans inﬂuence of the two phosphine groups can be considered constant throughout the series, conse- quently 1 J PtP of the various derivatives give an insight of the cis inﬂuence of X and Y. A second paper [14] dealt with the cis-[PtXY(PPh 3 ) 2 ] isomers (type B of Scheme 1). Here each P atom experiences the cis inﬂu- ence of a PPh 3 group, the trans inﬂuence of X and the cis inﬂuence of Y (or the other way round). Assuming that the mutual cis inﬂu- ence of the two phosphine groups is constant, the 1 J PtP values of each P nucleus depends on the cis and trans inﬂuences of X and Y. We have been able to discriminate the two inﬂuences, showing that the former, although of lower importance, is by no means irrelevant and must be taken into account when rationalising 1 J PtP as well as Pt–P bond distances. We could also justify the sequences of both inﬂuences in terms of Pt–P bonding and charge on Pt [14]. We were also interested in quantifying the inﬂuences, i.e. to ascertain ‘‘how much” a given X (or Y) ligand inﬂuences the Pt–P bonds cis or trans to such ligand, in other words the cis or trans 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.07.002 * Corresponding author. ** Corresponding author. E-mail address: alessandro.pasini@unimi.it (A. Pasini). Inorganica Chimica Acta 363 (2010) 3498–3505 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica