The comparative reactivity properties of previously reported trans-(dfmp)2Pt(Me)X (dfmp = (C2F5)2MeP; X = O2CCF3, OTf, OSO2F) with small molecules are presented. Anionic ligand displacement by CO ...depends upon X and the corresponding acid solvent. In trifluoroacetic acid, treatment of trans-(dfmp)2Pt(Me)(O2CCF3) with CO results in loss of dfmp to form the mixed phosphine/carbonyl product (dfmp)(CO)Pt(Me)(O2CCF3). However, in triflic and fluorosulfonic acids trans-(dfmp)2Pt(Me)(X) compounds react with CO to form trans-(dfmp)2Pt(Me)(CO)+(X)-. trans-(dfmp)2Pt(Me)(X) systems react with H2 under both acidic and aprotic conditions to form trans-(dfmp)2Pt(H)(X); trans-(dfmp)2Pt(H)(OTf) has been crystallographically characterized. Treatment of trans-(dfmp)2Pt(H)(OTf) with CO or dfmp gives trans-(dfmp)2Pt(H)(CO)+ or (dfmp)3Pt(H)+, respectively. In contrast to trans-(dfmp)2Pt(Me)(OTf), which releases methane in HOTf, trans-(dfmp)2Pt(Me)(OSO2F) in FSO3H at 80 °C cleanly produces the reductive elimination product MeOSO2F. Carbonylation of trans-(dfmp)2PtMe(CO)+X- under 1000 psi CO in turn cleanly produces MeC(O)X at ambient temperatures. The mechanism of reductive elimination from these Pt(II) precursors is discussed.
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A 1:1 addition of Ph2PCl to an ethereal solution of C2F5Li (formed from the reaction of BuLi with C2F5Cl) yields Ph2P(C2F5)(abbreviated pfepp) (1). The introduction of a fluoroethyl group results in ...a phosphine with electronic characteristics that approximate phosphites, bridging the electronic gap between traditional donor phosphine ligands and more electrophilic phosphine ligands like PhP(C2F5)2 (2). The pfepp ligand 1 is isolated as a high boiling liquid, which crystallizes upon standing at room temperature in an inert atmosphere. A series of Pt(II) complexes of the type trans-L2PtCl2 (L = pfepp 3; PhP(C2F5)2 4) have been prepared and structurally characterized by multinuclear NMR, IR and X-ray crystallography. The crystal structure of is the first example of a structurally characterized monodentate phosphine with a pentafluoroethyl pendant group.
The crystal structure of the bis-ethylene pincer complex (CF3PCP)Ir(C2H4)2 and calculations of ethylene rotational dynamics using DFT methods are presented. Comparisons to known bis-ethylene TBP ...complexes show that discrete rotational barriers for equatorial and axial ethylene ligands are unprecedented. Display omitted
The successful isolation and structural characterization of (CF3PCP)Ir(C2H4)2 is reported, which confirms a rare example of axial and equatorial ethylene coordination in a TBP coordination environment. DFT studies indicate a moderate barrier to ethylene rotation for the equatorial C2H4 group (ΔG‡=19.0kcalmol−1), and a negligible rotational barrier for the axial C2H4 (ΔG‡=1.2kcalmol−1). DFT analyses of ethylene rotational barriers for a series of known symmetrical (equatorial/equatorial) and asymmetric (equatorial/axial) bis ethylene Ir(I) complexes are consistent with previously reported experimental rotational barriers. In the case of the asymmetric systems (9aneS3)Ir(C2H4)2+ and (Tp)Ir(C2H4)2, a separate equatorial C2H4 rotational barrier is not observed due to facile conformational exchange of axial and equatorial ethylene coordination sites. Conformational exchange is not observed for (CF3PCP)Ir(C2H4)2.
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A series of complexes (dmpe)Pt(X)2 (X = Me, Cl, O2CCF3, OTf) have been prepared and their thermal stabilities examined. In contrast to (dmpe)Pt(Me)(Cl), which is stable up to 150 °C in benzene ...solution, thermolysis of (dmpe)Pt(Me)(O2CCF3) in benzene at 125 °C results in methane loss and the formation of (dmpe)Pt(Ph)(O2CCF3) as the major product, along with small amounts of the disproportionation products (dmpe)Pt(O2CCF3)2 and (dmpe)Pt(Ph)2 (8−10%). Kinetic studies in C6H6 and C6D6 indicate that the disappearance of (dmpe)Pt(Me)(O2CCF3) is first-order, with an overall kinetic isotope effect of 3.3(2). Methyl/aryl metathesis rates are not inhibited by added TBA+O2CCF3 -. Thermolysis of (dmpe)Pt(Me)2 in benzene at 180 °C for 18 h gave a mixture of unreacted (dmpe)Pt(Me)2 (15%), (dmpe)Pt(Me)(Ph) (51%), and (dmpe)Pt(Ph)2 (34%). Thermolysis of (dmpe)Pt(Me)(O2CCF3) in either 1,2- or 1,4-difluorobenzene at 125 °C afforded 2:1:1 statistical mixtures of (dmpe)Pt(Ar)(O2CCF3), (dmpe)Pt(Ar)2, and (dmpe)Pt(O2CCF3)2 (Ar = 2,3-C6H3F2 or 2,5-C6H3F2, respectively). Thermolysis of (dmpe)Pt(Me)(O2CCF3) in toluene affords a mixture of ortho, meta, and para tolyl products, (dmpe)Pt(C6H4Me)(O2CCF3). The metathesis rate for polar 1,2-difluorobenzene is not significantly different than that observed for the nonpolar aromatic substrates. Surprisingly, the aryl/aryl exchange rates for (dmpe)Pt(Ph)(O2CCF3) in C6D6 and C7D8 are 10−20 times faster than observed methyl/aryl exchange rates. These data may be accommodated by a mechanism involving a rate-limiting addition of aryl C−H bonds directly to a 4-coordinate (dmpe)Pt(II) or a 3-coordinate (η1-dmpe)Pt(II) center.
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An extension of prior protonolysis studies of platinum−carbon bonds to in situ generated Pt−C(sp2) bonds is reported. A series of (dfepe)Pt(η2-RC⋮CR‘) complexes (R = Me, R‘ = H; R = tert-butyl, R‘ = ...H; R = Me3Si, R‘ = Me; R = Ph, R‘ = Me; R = R‘ = Me; R = R‘ = Ph) have been prepared by treatment of (dfepe)Pt(μ-H)2 with the corresponding alkyne in order to examine the addition of Brønsted acids to form the alkenyl complexes (dfepe)Pt(C(R‘)C(H)R)(X). In the case where RC⋮CR‘ = propyne, a small (5%) amount of the propyne-bridged dimer (dfepe)Pt2(μ-η2:η2-MeC⋮CH) was also formed which could be prepared in pure form by the thermolysis of (dfepe)Pt(η2-HC⋮CMe) (1) at 90 °C. Dissolution of 1 in FSO3H at −80 °C produced the double-proton-transfer propene adduct (dfepe)Pt(η2-H2CC(H)Me)(X)+, without evidence for a propenyl Pt(II) intermediate. In contrast, dissolution of 1 in FSO3D at −80 °C cleanly produced the fully deuterated propenyl complex (dfepe)Pt(C(D)C(D)CD3)(OSO2F), which was characterized by 31P and 13C NMR. The direct observation of this initial proton-transfer intermediate in deuterated acid is ascribed to an unusually large kinetic isotope effect for the second proton-transfer step.
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The first examples of structurally-characterized 2- and 3-coordinate Pt(0) complexes with π-acceptor perfluoroalkylphosphine ligands (PFAP’s) is reported. Addition of ethylene to (dfebp)2Pt ...(dfebp=(C2F5)2PtBu) results in facile and reversible equilibria with the ethylene adducts (dfebp)2Pt(C2H4) and (dfebp)Pt(C2H4)2. Display omitted
The synthesis and structural characterization of 2- and 3-coordinate Pt(0) complexes with π-acceptor perfluoroalkylphosphine ligands (PFAP’s) is reported. (dfebp)2Pt (dfebp=(C2F5)2PtBu) was prepared in moderate yield by either thermolysis of (cod)Pt(Ph)2 in neat dfebp or, more efficiently, by the treatment of (nbe)3Pt with 2equiv. dfebp in the presence of H2. Addition of 1equiv. CF3CO2H to (dfebp)2Pt generates the expected Pt(II) trans-(dfebp)2Pt(O2CCF3)(H) product, while treatment with the mesitylenium acid (C6Me3H4)+B(C6F5)4− leads to phosphine loss and formation of the arene complex (η6-C6Me3H3)Pt(dfebp)(H)+(B(C6F5)4)−. Addition of ethylene to (dfebp)2Pt results in facile and reversible equilibria with the ethylene adducts (dfebp)2Pt(C2H4) and (dfebp)Pt(C2H4)2, which have been quantified by VT NMR spectroscopy.
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Treatment of the iridacyclopentadiene complex (1, R = CO2CH3) with silver tetrafluoroborate, followed by addition of a terminal alkyne (ethyne, ethyl ethnynyl ether, methyl propargyl ether), yields ...iridium(III) aryl-hydride complexes (6-H, R1 = H; 6-OEt, R1 = OCH2CH3; 6-CH2OMe, R1 = CH2OCH3). The structure of 6-OEt was established by X-ray crystallographic analysis. Treatment of 6-H with either HCl or carbon monoxide results in demetalation to give tetramethyl 1,2,3,4-benzenetetracarboxylate C6(CO2Me)4H2. When 3-butyn-2-ol and propargyl alcohol are employed as substrates, a similar reaction occurs with 1/AgBF4 to produce the phthalimidyl complexes (7-H, R1 = H; 7-Me, R1 = CH3). The lactone ring in 7 is generated from an intramolecular transesterification of the hydroxyl with an adjacent methyl ester. In all cases these products are attributed to tandem cycloaromatization and orthometalation processes.
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