Electron‐poor 2,3‐Dihydro‐1,3‐Diborolyl Complexes of Iron and Ruthenium: Synthesis, Reactivity, and Crystal and Electronic Structures of an Iron Sandwich Complex

Abstract

The addition product of sodium hydride and the 2,3-dihydro-1,3-diborole (CiPr) (BEt) CHMe (3c) reacted with [{(C Me )FeCl} ] to produce the green sandwich complex [(C Me )Fe{n -(CiPr) (BEt) CMe}] (2 c), which formally contains 16 valence electrons (VE). Complex 2c has unexpected structural properties in the solid state: the 1,3-diborolyl ring is extremely folded (41°), and the Fe-C2 distance is short (1.90 Å). Analogously, violet Ru complexes 4a,c,d were obtained from 3a,c, NaH or tBuLi, and [{(C Me )RuCl} ]. With the less bulky heterocycles 3 b,e the new 30 VE triple-decker complexes [(C Me )Ru{μ,n -(CR ) (BR ) CMe}RuH(C Me )] (5b,e) were formed, which contain a Ru-H bond. Cyclic voltammetric studies revealed the existence of stable anions 2c and 4d formed by reversible one-electron reduction at -1.26 and -1.40 V, respectively (vs. SCE). The red-brown anions were further characterized by ESR spectroscopy following stepwise reduction of the neutral species with potassium in THF. Addition of CO to 4a and 4d led to formation of the monocarbonyl complexes [(C Me )Ru(CO){n -(CR ) -(BR ) CMe}] (6a,d), and 6d was characterized by X-ray structure analysis. The heterocycle in 6d is less folded (19°) than in 2 c. Its CO ligand causes a 28.5° tilt of the cyclic ligands. Reaction of CO with 2 c yielded a red product of unknown structure. The electronic structure of 2 was studied by EH-MO theory, which revealed a unique bonding in the sandwich. The s̀ electron density of the B-C bonds participates in the bonding to the iron atom; this demonstrates that the number of bonding electrons is the same as in ferrocene. Thus, the complexes 2 actually have 18 VE.

Reactivity of electron-poor decamethyl-1,3-diboraruthenocene with sulfur and phosphorus compounds

“…The composition of the closo-cluster 4 was deduced from spectroscopic data and an X-ray structure analysis (see below). Attempts to synthesize 4 by various routes [3] led instead to the isomeric closo-cluster/triple-decker 4 0 , which had been obtained initially by reacting [(C 5 Me 5 )RuCl] 4 with an excess of NaH in the presence of the 1,2,3,4,5-pentamethyl-2,3-dihydro-1,3-diborole heterocycle [2]. …”

“…The electron-poor sandwich compound 1, which is presumed to be folded along the BÁ Á ÁB vector like the corresponding iron compound (ca. 41°), forms donoracceptor compounds with CO [2] and isonitrile [1], and a classic dihydride complex with H 2 . A complex reaction between BH 3 Á thf and 1 leads to (1,2,3,5,6-pentamethyl-4-hydro-2,3,5-tricarbahexaboranyl)(g 5 -pentamethylcyclopentadienyl)ruthenium [1] (2), which is formed by oxidative addition of BH 3 to 1, followed by HB-HÁ Á ÁBMe interaction and migration of this BMe group to the apical position and BH to the basal position of the pyramidal ligand (Scheme 1).…”

Paramagnetic (1,3‐Diborolyl)ruthenium Triple‐Decker Complexes and Transformation into Diamagnetic Complexes Having Bridging 1,3‐Diborafulvene Ligands

“…The complex is highly reactive toward Lewis bases, oxidative addition as well as stacking and insertion reagents. [7][8][9] Recently, a new method for the synthesis of 2a has been reported by treating [Cp*RuCl] 4 with pentamethyl-2,3-dihydro-1,3-diborole (1aH) in the presence of zinc, [10] which also led to three dinuclear products: the triple-decker complexes [(Cp*Ru) 2 {µ-1,3-(CMe) 3 (BMe) 2 2 }] (3c). The former complex slowly reacts with oxygen, which results in the transformation of 3b into the diamagnetic µ-dihydro-1-methylenediborafulvene triple-decker [(Cp*Ru) 2 {µ-η 5 :η 6 -(CMe) 3 (BCl)(BCH 2 )}] (4b).…”

Insertion of alkynes into the heterocycle of (η5-pentaalkyl-2,3-dihydro-1,3-diborolyl)(η5-pentamethylcyclopentadienyl)ruthenium: Formation and characterization of 4-borataborepine ruthenium complexes

“…We have reported on formally 16 VE (g 5 -pentaalkyl-2,3-dihydro-1,3-diborolyl)(g 5 -pentamethylcyclopentadienyl)iron complexes 1 [1,2] and its violet ruthenium analogs 2 [3,4] (e.g. 2a: R 1 = Me).…”