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• 93084-52-7 trans-Pt[Mn(CO)3Cp]2(PhCN)2 

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Comparison of two strategies toward the syntheses of platinum mixed-metal clusters. Reactivity of linear M-Pt-M and Mn-Pt-Mn complexes. X-ray crystal structures of Pt2M2(η5-C5H5) 2(μ3-CO)2(μ-CO)4(PEt 3)2 with M = Cr, Mo, and W

The new linear trimetallic complexes trans-Pt[M(CO)3Cp]2(PhCN)2 [M = Cr (1a), Mo (2a), W (3a)] have been isolated and characterized. The isocyanide complexes trans-Pt[Cr(CO)3Cp]2(t-BuNC)2 (1b) and Trans-Pt[Cr(CO)3Cp]2[c-C6H11NC] 2 (1c) have also been prepared because they are related to 1a. The first reported v(Pt-Cr) frequencies are 173, 174, and 177 cm-1 for 1a-c, respectively. The complex trans-Pt[Mn(CO)5]2(PhCN)2 (4a) has also been synthesized. It reacts with PPh3 to give the Pt5(CO)6(PPh3)4 cluster and with CO to afford the linear trimetallic trans-Pt[Mn(CO)5]2(CO)2 (4d) complex. The syntheses, characterizations, and X-ray structures of a family of new heterotetrametallic clusters Pt2M2Cp2(CO)6(PR3) 2 [Cp = η5-C5H5; M = Cr (5), Mo (6), W (7); R = Me (e), Et (f), n-Bu (g), Ph (h)] are described. Two different synthetic routes have been shown to lead to these clusters. In method A, the PtCl2(PR3)2 complexes were reacted with 2 equiv of Na[M(CO)3Cp] in THF. A complex redox reaction occurs, accompanied by ligand transfer and cluster formation. Thus, the dimers [M(CO)3Cp]2 and/or derivatives thereof such as the new Mo2(CO)5(PMe3)Cp2 were obtained, together with the mixed-metal clusters in which only one PR3 ligand is coordinated to each Pt atom. Method B involves the reaction in THF of 1 equiv of phosphine with the linear trimetallic complexes 1a-3a. Substitution of PhCN for PR3 induces a fragmentation of the complex into reactive units that combine with each other, affording the stable compounds. Mechanisms involving radical intermediates are proposed for these reactions. In general, method B presents significant advantages over method A, namely (i) higher cluster yield (up to 87%), (ii) a readily available stable platinum precursor, and (iii) generality and economy of introduction of a phosphine ligand into a cluster molecule. An X-ray diffraction study has been performed on the complexes Pt2M2Cp2(μ3-CO) 2(μ-CO)4(PEt3)2 [M = Cr (5f), Mo (6f), W (7f)]. Data for 5f: monoclinic, space group P21/c with Z = 2, a = 10.765 (6) A?, b = 9.430 (4) A?, c = 17.450 (5) A?, β = 115.37 (2)°, ρ(calcd) = 2.13 g cm-3. For 2321 reflections with I > 3σ(I), R = 0.032. Data for 6f: triclinic, space group P1 with Z = 2, a = 10.026 (2) A?, b = 11.155 (4) A?, c= 15.126 (4) A?, α = 85.17 (2)°, β = 75.44 (2)°, γ = 84.33 (2)°, ρ(calcd) = 2.29 g cm-3. For 4574 reflections with I > 3σ(I), R = 0.051. There are two slightly different molecules, A and B, in the unit cell. Complex 7f crystallizes in two different monoclinic cells, of P21/n space group with Z = 2: a = 8.768 (7), 11.920 (2) A?; b = 14.147 (2), 12.930 (6) A?; c = 13.580 (6), 12.166 (3) A?; β = 77.96 (5), 61.72 (2)°; ρ(calcd) = 2.60 g cm-3; 2365, 1921 reflections with I > 3σ(I), R = 0.033, 0.085 for types A and B, respectively. All these structures are characterized by a planar, triangulated parallelogram framework for the metallic core. The center of symmetry of these molecules is at the middle of the Pt-Pt′ bond. This distance is rather short, ranging from 2.612 (1) (in 5f) to 2.677 (1) A? (in 6f A). The Pt-M distances have values of 2.748 (1) and 2.709 (1) A? for M = Cr and range from 2.777 (2) to 2.846 (1) A? for M = Mo and from 2.775 (1) to 2.836 (1) A? for M = W. A shorter Pt-M distance is found where the contributions of the bridging carbonyls on this bond is higher. In these 58-electron clusters, the 18-electron [CpM(CO)3]- fragments bridge the L→Pt(I)-Pt(I)←L unit in a very original way: a three-legged piano-stool structure with the two Pt atoms located within the M(CO)3 cone. Each PEt3 ligand is coordinated to a Pt atom with a Pt′-Pt-P angle between 169.7 (1) and 177.7 (1)° and an average Pt-P distance of 2.285 A?. The planes of the η5-Cp ligands are by symmetry parallel to each other and form a dihedral angle between 75.6 and 86.9° with the metallic plane. The carbonyl ligands C(1)O(1) and C(3)O(3) are semibridging the M-Pt′ and M-Pt edges, respectively, whereas C(2)O(2) is semi triply bridging the heterotrimetallic face MPtPt′. By symmetry, an identical geometry is found with the carbonyls bridging M′Pt,M′Pt′ and M′PtPt′. This bonding situation is compared in the Pt2Cr2, Pt2Mo2, and Pt2W2 clusters and related to the difference observed between the Pt-M and Pt′-M distances. Spectroscopic, IR, and 1H, 13C{1H}, and 31P{1H} NMR data indicate that all the Pt2M2 clusters presented here have the same basic structures as 5f, 6f, and 7f and that the solid-state structure is retained in solution. 1J(PtPt) values of 775 and 1039 Hz were found for 6g and 7g, respectively.