Comparative Rates of Ligand Substitution Reactions of Pt−C-Bonded Complexes in Aqueous Solution and the X-ray Crystal Structure of [Pt{C₆H₃(CH₂NMe₂)₂-2,6}(OH₂)][OSO₂CF₃]

Abstract

The substitution behavior of the organometallic complex cation [Pt{C 6 H 3 (CH 2 NMe 2 ) 2 -2,6}-(OH 2 )] + (1) has been studied with a series of nucleophiles (Cl -, Br -, I -, N 3 -, NCS -, thiourea, N, N′-dimethylthiourea, N,N,N′N′-tetramethylthiourea) as a function of nucleophile concentration ([Nu]), pH, temperature, and pressure. Complex 1 affords pseudo-first-order rate constants, k obs , for the complex-formation reaction given by k obs ) k 1 [Nu] + k -1 ; the k -1 term is due to the reverse aquation reaction and is insignificant for the stronger, S-donor nucleophiles. The mechanism for the substitution of the coordinated water molecule is associative, as demonstrated by the large negative values of ∆S q and ∆V q . The results are compared to those obtained earlier for the geometrically related neutral zwitterionic complex [Pt{C 6 H 4 (CH 2 NMe 2 )-2}(NC 5 H 4 SO 3 -3)(OH 2 )] (2). Both cyclometalated complexes 1 and 2 have very high substitution reactivities that can be ascribed to labilization which arises from the σ-bonded carbon atom of the ortho-metalated aryl ligand in combination with back-bonding to the in-plane aryl ligand that increases the electrophilic character of the Pt(II) center. In complex 1 the σ-donicity of the second chelating dimethylamine group and/or the increased chelation effect of the tridentate ligand lead to a significantly increased lability of the coordinated water molecule, compared to complex 2. The X-ray structure of the ionic complex [Pt{C 6 H 3 (CH 2 NMe 2 ) 2 -2,6}(OH 2 )] + [OSO 2 CF 3 ] -(1a) is described. The crystal structure comprises an aggregate of two complex cations and two triflate anions. The structure contains two fully equivalent square-planar coordinated Pt(II) centers with an O-ligated neutral H 2 O molecule (Pt-O ) 2.186 (2) Å) trans to the Pt-C aryl bond (Pt-C ) 1.903(2) Å); the aggregate results from the involvement of both H atoms of the two H 2 O molecules in asymmetric hydrogen bonding to O atoms of the two triflate anions.

Hydrogen Carbonate Inhibited and Induced Substitution Reactions of Labile Square‐Planar Diethylenetriaminepalladium(II) Complexes

“…(6) and is thus controlled by the fraction of aqua complex (Pd(L)H202') in Eq. (7), which results from the acid-base equilibrations (2) and (3) The observed increase in kobs with an increase in [C1-Ifre, (except for Pd(Me3dien)C1+ at pH=2.7 in Table 1 b as discussed later) is in agreement with Eq. (6).…”

“…This ratio is comparable Ref. [7,191 Ref. [7] a Single measured value used in kobs=kan ( 10-7~38/(10-7~38+10-7~54)] { 10"~4/(10"~4+10-7~'8)) (5x10-')+kaq (Eq.…”

“…[7,191 Ref. [7] a Single measured value used in kobs=kan ( 10-7~38/(10-7~38+10-7~54)] { 10"~4/(10"~4+10-7~'8)) (5x10-')+kaq (Eq. (20)) to calculated k,=34.7 dm' mol-' s-I (included in Table 5 ) with kaq=O.10 SKI taken from Fig.…”

“…3c Table 5 Rate constant for Pd(L)H202++ X & Pd(L)X2+ + H2O at 25 "C and I=O.I moVdm3 ionic strength k-x L X k8/dm3 mol-' s-I k-8IS-I Source dien TRIS 3240+60 -0 Ref. [7] uracil, U") Fig. 3 b Table 4 Ref.…”

Hydroxy- and Mercaptopyridine Pincer Platinum and Palladium Complexes Generated by Silver-Free Halide Abstraction

“…In NCN pincer Pt iodide complexes, it was previously found that the addition of polar, coordinating dimethylformamide (DMF) establishes an equilibrium in which there is partial displacement of the covalently bound iodide by a molecule of solvent, generating an ion pair. 12 The outer sphere iodide anion can then be exchanged for perchlorate (ClO 4 -) on an ion-exchange resin. We reasoned that alternate chemical reagents could be employed to force this equilibrium toward the ion-separated or halide-abstracted products.…”