Selective Synthesis of Osmanaphthalene and Osmanaphthalyne by Intramolecular CH Activation

Abstract

Metallabenzenes[1] and metallabenzynes [2] have attracted considerable research interest in recent years. However, their higher homologues are still very rare. [3] In fact, only two well-characterized examples have been reported. One is the metallanaphthalene prepared by Paneque et al. in 2003 by oxidation of a bicyclic iridium complex.[3a] The other is the metallanaphthalyne synthesized by Jia, Lin, and co-workers in 2007 by reduction of an osmium carbyne complex with zinc and subsequent CÀCl bond activation. [3b] It is known that CÀH activation [1a, 4] is a very important method for the synthesis of organic and organometallic compounds. Recently, we reported the synthesis of osmium hydride-alkenylcarbyne complex [OsH{ C À C(PPh 3 ) = CHPh}(PPh 3 ) 2 Cl 2 ]BF 4 (1) and its formal [4+2] cycloaddition with acetonitrile to give the first late-transition-metal-containing metallapyridine and metallapyridinium compounds.[5]From our further investigation of the reactivity of 1, we herein report the selective formation of metallanaphthalene 2 and metallanaphthalyne 3 from 1 in high yields by intramolecular C À H activation of the phenyl ring under a N 2 or O 2 atmosphere, respectively (Scheme 1). Furthermore, the transformation of isolated 2 into 3 is also reported. As there is a metallabenzene unit in 2 and a metallabenzyne unit in 3, the transformation of 2 into 3 represents the first example of the conversion from metallabenzene into metallabenzyne.Heating 1 in DCE (ClCH 2 CH 2 Cl) at reflux under a N 2 atmosphere gave the (m-Cl) 3 -bridged bisosmanaphthalene 2, which was isolated as a green solid in 72 % yield (Scheme 1). The structure of 2 was confirmed by X-ray diffraction. The asymmetric unit contains two independent molecules (2 A and 2 B). A drawing of the cation 2 A is shown in Figure 1. In 2 A, two osmanaphthalene metallacycles are connected by three chlorido bridges. The OsÀCl bond lengths of the chlorido bridges are in the range 2.496(2)-2.554(2) , which are similar to those in reported dinuclear osmium complexes with three chlorido bridges.[6] The mean deviation from the least-squares plane through the C11, C12, C13, C14, and C15 chain is 0.035 , and the value through the C21, C22, C23, C24, and C25 chain is 0.026 . The Os1 atom is out of the plane of the metallacyclic carbon atoms by 0.736 (the relevant value of Os2 is 0.697 ), which is similar to the metal atom displacement in the iridanaphthalene compound reported by Paneque et al. (0.76 ).[3a] The dihedral angle between the plane through C11, C12, C13, C14, and C15 and the plane constructed by C11, Os1, and C15 is 31.78 (the relevant dihedral angle in the Os2-containing six-membered metallacycle is 30.48). These values are comparable with those found in our previously reported bisruthenabenzene Scheme 1. Preparation of 2 and 3. Figure 1. X-ray crystal structure of 2 A (ellipsoids at the 50 % probability level).[12] Counteranion and phenyl rings in PPh 3 groups are omitted for clarity. Selected bond lengths []:

The Chemistry of Aromatic Osmacycles

“…Interestingly, 51 could even be obtained by directly heating the solid sample of 50 in air (Scheme 18). 44 The formation of 50 and 51 underwent a similar migration of the hydride ligand from the osmium center to the carbyne carbon atom. The subsequent ortho CÀH bond activation of the phenyl ring led to the formation of a hydride osmanaphthalene intermediate.…”

“…43 We discovered the synthesis of osmanaphthalene and osmanaphthalyne unexpectedly in 2009, when we studied the thermal and air stability of osmium hydride alkenylcarbyne 36. 44 Heating 36 in ClCH 2 CH 2 Cl under a N 2 atmosphere afforded the (μ-Cl) 3 -bridged bisosmanaphthalene 50, while under an O 2 atmosphere osmanaphthalyne 51 was produced. Interestingly, 51 could even be obtained by directly heating the solid sample of 50 in air (Scheme 18).…”

Synthesis and Reactivity of Iridacycles Containing the TpMe2Ir Moiety

“…Higher homologues of metallabenzenes were unknown until 49 was isolated, and they are still very rare; only last year a second metallanaphthalene was described in the literature, an osmanaphthalene, which transforms into an osmanaphthalyne, thus representing the first example of conversion of a metallabenzene into a metallabenzyne. [48] (iii) Finally, another iridabenzene 52, which has not been commented on in this review was formed by an acid-catalyzed migratory insertion of a vinylidene ligand into a Tp Me2 -iridacyclopentene derivative. [38] Because it had been predicted that π donors, especially those ortho and para to the metal, would stabilize aromatic metallacycles, [49] iridanaphthalene 49 and iridabenzenes 25, 28, 29, 30, 48 were unexpected in view of the presence of a considerable number of electron-withdrawing substituents on the ring, namely CO 2 Me.…”

A Metallaanthracene and Derived Metallaanthraquinone

“…the metallabenzofuran, I)and 2) those in which p-delocalization over the fused ring is not possible because at least one ring atom is saturated ((B), Scheme 2, e.g. [7] In addition, metallanaphthalenes of isomer b have been prepared through oxidation of af usedring iridacyclohexadiene, [8] by rearrangement of an osmium vinyl carbyne complex, [9] and by intramolecular CÀHa ctivation of ap henyl substituted alkenylcarbeneiridium complex. Compounds of class (B) in which one end of the fused ring is bound to the metal have been referred to as "tethered" metallabenzenes.…”