Reaction of 2,2'-bipyridine (bpy) with dirhodium carboxylates: mono-bpy products with variable chelate binding modes and insights into the reaction mechanism

Abstract

Synthetic procedures are described for the preparation of mono-2,2'-bipyridine (bpy) complexes possessing the Rh24+ core. Reaction of Rhz(OAc),(MeOH)2 (1) with 1 equiv of bpy in Me2CO produces Rhz(OAc)4(bpy) (3) in excellent yield. The compound crystallizes in the triclinic space group Pi with the following cell parameters at -172 'C: u = 9.883(3), b = 13.078(5), c = 8.323(2) A; a = 97.02(2), j 3 = 106.90(1), y = 94.29(2)'; Z = 2; V = 1015 As. The structure was solved by direct methods (MULTAN) and refined to values of conventional indices R (R,) of 4.72% (4.50%) using 2636 unique reflections with F,, > 3u(F0). The two Rh2+ centers are bridged by three q1:q1:p2AcO-groups over a Rh-Rh bond distanceof 2.475(2) A. The coordination spheres of Rh( 1) and Rh (2) are completed by chelating bpy and O A c groups, respectively. The chelating OAc-is asymmetrically bound as a consequence of the axialfequatorial positioning of its two oxygen atoms O (27) and O(29). Compound 3 undergoes a reaction on dissolution in MeOH to give [Rh2(OAc)3(bpy)(MeOH)](OAc).2MeOH (4) as determined by 'H NMR (1 D-and 2D-homonuclear J-resolved spectroscopy), elemental analysis, conductivity measurements, and reactivity studies. Reaction of Rh2(02CCF3)4(Me&0)2 (2) with 1 equiv of bpy in CHzClz, followed by recrystallization of the product from THFfH20, produces crystals of Rh2(02CCF3)4(bpy)(THF)(HzO).THF (5). Compound 5 crystallizes in the monoclinic space group Pc with the folowing cell parameters at -105 OC: u = 10.683(8), b = 9.170(8), c = 17.783(1) A; a! = 90.00, j3= 103.52(7), y = 90.00'; 2 = 2, V = 1693 The structure was solved by direct methods (MITHRIL) and refined to values of R (R,) of 5.1% (5.8%) using 2493 unique reflections with F > 3u(F). The two Rh2+ centers are bridged by two q1:q1:p2 02CCF3-ligands across a Rh-Rh separation of 2.520(3) A. Coordination about Rh(1) is completed by two terminal q1-0~CCF3-groups in equatorial sites with the axial site being occupied by a water molecule. Rh(2) is ligated by a chelating bpy group in the equatorial plane, with axial ligation being provided by a THF molecule. Reaction mixtures comprising [Rh2(0Ac)2(MeCN),j] (BF4)2 (6) and 1 equiv of bpy in MeCN lead to isolation of [R~~(OAC)~(~~~)(M~CN)~](BF~)~.M~CN (7). Compound 7 crystallizes in the triclinic space group Pi with the following cell parameters at -170 OC: u = 12.381(2), b = 14.301(2), c = 12.246(2) A; a! = 94.60(1), j 3 = 105.84(1), y = 117.42(1)'; 2 = 2; V = 1797 AS. The structure was solved by direct methods (MULTAN) and refined to values of R (R,) of 4.92% (5.74%) using 4723 unique reflections with F > 3 4 9 . The two metals are bridged by two cis q':q*:pz-OAcgroups that span a Rh-Rh distance of 2.5395(8) A. Coordination at Rh( 1) is completed by a chelating bpy in the equatorial plane and an axial MeCN ligand, while the coordination sphere of Rh(2) is completed by two equatorial MeCN molecules and an axial MeCN molecule.

Cationic dirhodium carboxylate-catalyzed synthesis of dihydropyrimidones from propargyl ureas

“…To test this assumption, we turned our attention to the cationic catalyst [Rh 2 (OAc) 2 (MeCN) 6 ][BF 4 ] 2 . 12 To our delight, this provided 2a in 94% isolated yield with no trace of the other three possible cyclization products observable by 1 H NMR.…”

Photochemistry and DNA photocleavage by a new unsupported dirhodium(II,II) complex

“…The recovered product was 0.11 g which is an overall yield of 75 per cent based on rhodium. Recrystallization of [Rh 2 (phen) 2 [65] and cis-[Rh 2 (μ-OAc) 2 (dppz) 2 (CH 3 OH)(OAc)] + [68].…”

Contrasting Reactivity of 2-Mesityl-1,8-Naphthyridine (Mes-NP) with Singly-Bonded [RhII–RhII] and [RuI–RuI] Compounds

“…The Rh-Rh distance (2.387(1) Å ) is the shortest [16] amongst similar paddlewheel Rh 2 (CH 3 COO) 2 complexes listed in Table 1. [17][18][19][20][21][22][23][24][25][26][27][28][29][30] It is our assertion that weak axial interactions lead to shorter metalmetal distance in compound 1. [8,9] The reaction of cis-[Ru 2 (CO) 4 (2) in high yield.…”