Oxidation of Half-Lantern Pt₂(II,II) Compounds by Halocarbons. Evidence of Dioxygen Insertion into a Pt(III)–CH₃ Bond

Abstract

The half-lantern compound [{Pt(bzq)(μ-N^S)}2] (1) [bzq = benzo[h]quinoline, HN^S = 2-mercaptopyrimidine (C4H3N2HS)] reacts with CH3I and haloforms CHX3 (X = Cl, Br, I) to give the corresponding oxidized diplatinum(III) derivatives [{Pt(bzq)(μ-N^S)X}2] (X = Cl 2a, Br 2b, I 2c). These compounds exhibit half-lantern structures with short intermetallic distances (∼2.6 Å) due to Pt-Pt bond formation. The halogen abstraction mechanisms from the halocarbon molecules by the Pt2(II,II) compound 1 were investigated. NMR spectroscopic evidence using labeled reagents support that in the case of (13)CH3I the reaction initiates with an oxidative addition through an SN2 mechanism giving rise to the intermediate species [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}]. However, with haloforms the reactions proceed through a radical-like mechanism, thermally (CHBr3, CHI3) or photochemically (CHCl3) activated, giving rise to mixtures of species [X(bzq)Pt(μ-N^S)2Pt(bzq)R] (3a-c) and [X(bzq)Pt(μ-N^S)2Pt(bzq)X] (2a-c). In these cases the presence of O2 favors the formation of species 2 over 3. Transformation of 3 into 2 was possible upon irradiation with UV light. In the case of [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}] (3d), in the presence of O2 the formation of the unusual methylperoxo derivative [I(bzq)Pt(μ-N^S)2Pt(bzq)(O-O(13)CH3)}] (4d) was detected, which in the presence of (13)CH3I rendered the final product [{Pt(bzq)(μ-N^S)I}2] (2c) and (13)CH3OH.

A Cyclometalated N‐Heterocyclic Carbene: The Wings of the First Pt2(II,II) Butterfly Oxidized by CHI3

“…The Pt−Pt distance in 3 (2.6324(3) Å) is slightly longer than that in 2 (2.6079(2) Å) (see Table ), likely due to the larger trans influence of the CHI 2 fragment when compared to the I one. The Pt−I distances are also in the range of those found in other Pt III complexes ,,. In the two complexes, 2 and 3 , the “Pt(EtO 2 C‐C^C*)” metallocycles display an anti ‐arrangement of the Pt−C* bonds (C1‐Pt1‐Pt2‐C14 torsion angles are 82.25(17)° 2 and 79.65 (31)° 3 ), the six‐membered ring Pt 2 N 4 has the typical boat‐like conformation (the angle between the Pt‐N‐N‐Pt fragments being 89.25(6)° for 2 and 89.32(9)° for 3 ).…”

“…Compounds 2 and 3 were fully characterized (see Experimental Section, Figures , , and and Figures S7–S19 in Supporting Information). Their X‐ray structures showed for both, 2 and 3 (see Figure ) the expected boat‐like shape of the molecule and also, the shortening of the intermetallic distance ( d Pt−Pt : 2.6079(2) Å 2 , 2.6324(3) Å 3 ) with respect to 1 due to the formation of a Pt III −Pt III bond . These distances are shorter than the observed in the mixed‐valent Pt III Pt III Pt II complex [Pt 3 Br 2 (μ‐pz) 6 ] ( d Pt(III)‐Pt(III) =2.7787(8) Å) .…”

“…Their X-ray structures showed for both, 2 and 3 (see Figure 2) the expectedb oat-like shapeo ft he molecule and also, the shortening of the intermetallic distance (d PtÀPt :2 .6079(2) 2,2 .6324(3) 3)w ith respect to 1 due to the formation of aP t III ÀPt III bond. [12,14,20] These distances are shorter than the observed in the mixed-valent Pt III Pt III Pt II complex [Pt 3 Br 2 (m-pz) 6 ]( d Pt(III)-Pt(III) = 2.7787 (8) ). [21] In these complexes each Pt III center has adistortedo ctahedral environment with the axial positions occupiedb ya n Xf ragment (I 2,Iand CHI 2 3)a nd the other Pt III center with the X-Pt-Pt angles close to 1658.T he PtÀ Pt distance in 3 (2.6324(3) )i sslightly longer than that in 2 (2.6079(2) )( see Ta ble 2), likely due to the larger trans influence of the CHI 2 fragment when compared to the Io ne.…”

“…To our knowledge, two‐center two‐electron [2c, 2e] oxidation processes of Pt 2 (II,II) complexes with halocarbons (RX) to give the corresponding Pt 2 (III,III)X 2 or Pt 2 (III,III)RX have been described for lantern‐ or half‐lantern complexes, such as [Pt(pop) 4 ] 4− (pop=pyrophosphite), [Pt 2 (pyt) 4 ], [Pt 2 (ppy) 2 (pyt) 2 ], and [Pt 2 (bzq) 2 (μ‐N^S) 2 ], all of them with intermetallic distances of ca. 2.9 Å.…”

“…[7] In the case of pyrazolate-bridged dinuclearP t II complexes,t he chemistryh as been focused on butterfly-like complexess uch as [{Pt(N^N)(m-Rpz)} 2 ]( N^N = diimineso rp yridylpyrazolate), [8] [{Pt(C^N)(m-Rpz)} 2 ]( C^N:C ,N-cyclometalated ligand) [9] and [{Pt(C^C*)(m-Rpz)} 2 ] [10] due to their phosphorescent behavior.M any studies addressed the control of the bulkiness of the pyrazolateb ridge (the butterfly body) and the bulk and electronic properties of the C^N (the butterfly wings), as the way to control the Pt···Pt distance and then, the nature of the emissive state ( 3 IL/ 3 MLCT or 3 MMLCT) and the color of the emission (from greenish-blue to orangish-red). [9] To our knowledge,t wo-center two-electron[ 2c, 2e] oxidation processes of Pt 2 (II,II) complexes with halocarbons (RX) to give the corresponding Pt 2 (III,III)X 2 or Pt 2 (III,III)RX have been describedf or lantern-or half-lantern complexes, such as [Pt(pop) 4 ] 4À (pop = pyrophosphite), [11] [Pt 2 (pyt) 4 ], [12] [Pt 2 (ppy) 2 (pyt) 2 ], [13] and [Pt 2 (bzq) 2 (m-N^S) 2 ], [14] all of them with intermetallic distances of ca. 2.9 .H owever,f or bis-pyrazolate complexes, [8, 9a-c, 15] with intermetallic separations ranging from 3.4863(6)t o3 .0457 (7) (except in complex with C^N = 2-(2,4difluorophenyl)pyridyl and Rpz = 3,5-bis(tert-butyl)pyrazolate, d Pt··Pt = 2.8343(6) ), this kind of reaction has been never reported.…”