Aromatic Iridacycles

Abstract

The first example of a family of related aromatic metallacycles has been synthesized, and the physical and chemical properties of its individual members have been investigated. The metallacyclic rings in these compounds are, in general, constructed from pentadienyl- or heteropentadienyliridium precursors via C-H bond activation processes. The molecules display the structural and spectroscopic features of aromaticity, including ring planarity, pi-bond delocalization, and diamagnetic ring current effects. The reactivity profile of the molecules is complex, reflecting the simultaneous presence of an aromatic ring and a reactive metal center.

Planar Möbius aromatic pentalenes incorporating 16 and 18 valence electron osmiums

“…2, in which Os1 À C4 is always a single s-bond, similar to the previous observation in osmapentalynes 19 . Distances of C À C bonds (1.365-1.414 Å) of the fused five-membered rings are between C À C single-and double-bond lengths, indicating a delocalized structure [33][34][35][36][37][38][39][40][41][42] . Complex 3-(BF 4 ) 2 was further characterized by 1 H, 31 P and 13 C NMR spectroscopy.…”

Is the Hoveyda–Grubbs Complex a Vinylogous Fischer‐Type Carbene? Aromaticity‐Controlled Activity of Ruthenium Metathesis Catalysts

“…In this respect the concept of metalloaromaticity19 introduced by Calvin and Wilson in 194520 is richly evoked to explain the properties of organometallic compounds in terms of their stability, reactivity and structure. Numerous studies were conducted in this field for example, synthesis of classes of iridacycles,19b,c ferrabenzenes,21 ruthenabenzenes,22 molybdafuranes,23 as well as simple acac24 and diimine complexes 19d. At this moment we realized that aromatic stabilization of the chelate may be responsible for the unexpected lack of reactivity of complexes 4 a and 4 c , which operate at the initiation step (stabilizes the chelate for the dissociation20, 25 or retards the reaction with the olefin in an associative26 mechanism) and may justify the pronounced “on/off” effect in the catalytic activity as amplifying small energetic differences by the kinetic pattern of the precatalyst activation process.…”

Formation of 5-membered metallacycles at iPrPCPIr by C–H, O–H, and C–CO bond cleavage

“…For example, metallacycles have been determined as key intermediates in olefin metathesis reactions [3,4], a number of C-H functionalization reactions [5][6][7][8][9], and alkyne trimerisation [10,11]. The chemistry of iridacycles is quite diverse [12][13][14]. Complexes containing iridium metallacycles have been used for OLED applications [15], the hydrogenation of imines [16], the conversion of ethanol to butanol [17], and have even shown anti-cancer activity [18].…”