Synthesis and Comparative η¹-Alkyl and Sterically Induced Reduction Reactivity of (C₅Me₅)₃Ln Complexes of La, Ce, Pr, Nd, and Sm

Abstract

The synthesis of (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr from [(C 5 Me 5 ) 2 Ln][(µ-Ph) 2 BPh 2 ] and KC 5 Me 5 completes the series of sterically crowded (C 5 Me 5 ) 3 Ln complexes for the larger lanthanides, La-Nd and Sm, and allows a comparison of structure and reactivity as a function of metal size. Synthesis of these new (C 5 Me 5 ) 3 Ln complexes required silylated glassware, which surprisingly was not necessary for the more sterically crowded analogues. (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr display longer Ln-C(C 5 Me 5 ) distances than any previously described Ce or Pr complexes containing the (C 5 Me 5 )ligand. The η 1 -C 5 Me 5 alkyl-like reactivity of the (C 5 Me 5 ) 3 Ln complexes was investigated with CO, ethylene, THF, and H 2 . The sterically induced reduction (SIR) reactivity of the (C 5 Me 5 ) 3 Ln complexes was examined with SedPPh 3 , AgBPh 4 , C 8 H 8 , and phenazine. All of these data indicate that (C 5 Me 5 ) 3 Ln reactivity increases with decreasing size of the metal and hence increased steric crowding. The reactivity of (C 5 Me 5 ) 3 Ln with CO 2 and with Et 3 NHBPh 4 was examined since each substrate could react by either η 1 -C 5 Me 5 alkyl or SIR pathways. In both cases, alkyl-like reactivity is observed: CO 2 forms the insertion product (C 5 Me 5 ) 2 Ln(O 2 CC 5 Me 5 ), containing a carboxylate with a pentamethylcyclopentadiene substituent, and Et 3 NHBPh 4 forms [(C 5 Me 5 ) 2 Ln][(µ-Ph) 2 BPh 2 ] and C 5 Me 5 H. The reactions of (C 5 Me 5 ) 3 Sm with aryl halides and primary alkyl halide radical clocks (RX) yield C 5 Me 5 R, C 5 Me 5 X, (C 5 Me 5 ) 2 , R-R, and [(C 5 Me 5 ) x SmX y ] z as products, which indicate that SIR is not the only reaction pathway with these substrates. The X-ray crystal structures of the (C 5 Me 5 ) 3 Ln reaction products [(C 5 Me 5 ) 2 La] 2 (µ-η 2 :η 2 -Se 2 ), [(C 5 Me 5 ) 2 (THF)La] 2 (µ-η 2 :η 2 -Se 2 ), [(C 5 Me 5 ) 2 La] 2 (µ-η 3 :η 3 -C 12 N 2 H 8 ), [(C 5 Me 5 ) 2 Sm(µ-I)] 3 , and (C 5 Me 5 ) 2 Sm(O 2 CC 5 Me 5 ) are described as well as a new synthesis of (C 5 Me 5 ) 3 Sm from (C 5 Me 5 ) 2 Sm and (C 5 Me 5 ) 2 .

C–H bond activation through steric crowding of normally inert ligands in the sterically crowded gadolinium and yttrium (C 5 Me 5 ) 3 M complexes

“…The reactivity of (C 5 Me 5 ) 3 Gd vis-à-vis (C 5 Me 5 ) 3 Sm was of interest to determine whether the sterically more crowded complex of the smaller metal would have higher reactivity. Previously, it had been observed that the larger metals, La-Nd, which generate the less sterically crowded complexes, are less reactive than Sm (8). However, because Sm often has special reactivity because of the presence of its divalent state, Sm 2ϩ (2,11,12), it was important to examine the metal size͞reactivity relationship with both larger and smaller metals.…”

“…Such syntheses required developing reactions that did not depend on the Sm(II) reactivity shown in Scheme 1. Successful syntheses of (C 5 Me 5 ) 3 Ln complexes of the larger metals, La (1.216 Å) (17) (8).…”

“…These complexes would be more sterically crowded and presumably more reactive. Because the synthesis of some of the less crowded complexes had proven difficult, e.g., (C 5 Me 5 ) 3 La, (C 5 Me 5 ) 3 Ce, and (C 5 Me 5 ) 3 Pr required the use of silylated glassware for isolation (8,17), it was uncertain whether more crowded, presumably more reactive (C 5 Me 5 ) 3 Ln complexes could be made. The next smaller metal, Eu, was not an alternative because Eu(III) is reported to be reduced by (C 5 Me 5 ) 1Ϫ and would not be expected to be stable (19).…”

Remarkable Stability of Metallocenes with Superbulky Ligands: Spontaneous Reduction of SmIII to SmII

“…(4)]. [24] This result implies that the first step in SIR of [ 2 M] (M = Ca, Yb, Sm) crystallize isomorphously in space group P1 with the metal ion on the center of inversion (Figure 1). Considering the presence of many n-butyl substituents, the structures are surprisingly ordered and of good quality.…”

Activation of Heteroallenes COxS2–x (x = 0–2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex

“…This reactivity profile is novel as only a handful of Sm II complexes have previously been shown to promote oxalate product formation, [19,20] and CO 2 insertion into a Sm-ligand bond is rare. [19,28] In order to shed some light on this peculiar reactivity as well as to determine some plausible reaction pathways, DFT calculations (B3PW91) were undertaken on the reaction of 1 with CS 2 , CO 2 , and COS. The reaction with CS 2 was first investigated.…”