Synthesis and Photoisomerization of Divinyltetramethyldisiloxane and Divinyltetramethyldisilazane Complexes of (η⁵-C₅R₅)Rh (R = H, Me). Crystal and Molecular Structure of (η⁵-C₅Me₅)Rh[η⁴-(CH₂CH)Me₂SiOSiMe₂(CHCH₂)]

Abstract

The synthesis and photochemistry of a series of new rhodium complexes of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, (CH2CHSiMe2)2O, and its disilazane analogue (CH2CHSiMe2)2NH are reported. The divinyldisiloxane or divinyldisilazane ligands in (η5-C5R5)Rh[η4-(CH2CHSiMe2)2X] (R = H, Me; X = O, NH; type 1 complexes) are coordinated through the vinyl groups as for a diene. The structure of (η5-C5Me5)Rh[η4-(CH2CHSiMe2)2O] was established crystallographically. The two coordinated double bonds are arranged with their Si substitutents in a cis orientation with respect to the metal. The strain in the structure is suggested by the scissor geometry of the vinyl CC bonds relative to the C5 plane of the ring, combined with unequal Rh-C and CC bond lengths. Photolysis of (η5-C5R5)Rh(C2H4)2 (R = H, Me) in the presence of (CH2CHSiMe2)2X (X = O, NH) results in the formation of the complexes of type 1, together with an isomer in which the substituents on the coordinated CC bonds are oriented trans at rhodium (2) and species containing two dangling divinyldisiloxane ligands, (η5-C5R5)Rh[η2-(CH2CHSiMe2)2X]2, in both cis and trans configurations. Direct irradiation of species of type 1 converts them to the photoisomer 2. The 16-electron intermediate with one η2-divinyldisiloxane ligand may be trapped by addition of CH2CHSiMe3 or excess (CH2CHSiMe2)2X (X = O, NH). The isomerization of type 2 species to type 1 species proceeds by first-order kinetics. For trans-(η5-C5H5)Rh[η4-(CH2CHSiMe2)2O] (2a) the values of ΔH ⧧ and ΔS ⧧ are 114 ± 1 kJ mol-1 and 41 ± 4 J mol-1 K-1, consistent with rate-determining dissociation of one double bond. Replacement of C5H5 by C5Me5 increases H ⧧ by 9 ± 2 kJ mol-1. The assignment of the photoisomers 2 as the trans species is supported by further observations that (i) a mixture of 1 and 2 can be synthesized by hydrolysis of chlorovinylsilane precursors (η5-C5H5)Rh(η2-CH2CHSiMe2Cl)2, a method which generates the Si−O−Si linkage in situ, (ii) the conformationally locked species with a cyclic trivinyltrimethyltrisiloxane ligand, (η5-C5H5)Rh[η4-(CH2CHSi(Me)O)3], does not undergo photoisomerization, and (iii) the species with the Si−O−Si linkage replaced by a C−O−Si linkage (η5-C5H5)Rh[η4-(CH2CMe)CH2OSiMe2(CHCH2)] also fails to undergo photoisomerization. These complexes represent the first examples of adoption of a trans configuration at a metal by η4-divinyldisiloxane ligands and the first examples of this type of isomerization.

Synthesis of ansa-Zirconocene/Rhodium Heterobimetallic Complexes: Enhanced Catalytic Activity in Stereospecific Polymerization of α-Olefins

“…The crystal structure of 3b was determined by X-ray diffraction analysis (Figure ). The bond lengths of the vinyl carbons (C1−C2 1.407(4) Å, C3−C4 1.402(4) Å) were longer than those observed in 1 (C1−C2 1.307(4) Å, C3−C4 1.284(4) Å; Figure ) and similar to those reported in other rhodium−olefin complexes . The angle of C1−Si−C3 (99.0(1)°) in 3b is smaller than the one observed in 1 (109.8(1)°) due to coordination to rhodium.…”

The synthesis and characterisation of some nickel(0) complexes with π-bounded vinylsilicon ligands; the molecular structure of [Ni{P(C6H5)3}2{η2-CH2CHSi(CH3)3}]

“…High reactivity of this complex has led to synthesis of other Pt(0) complexes containing both divinyltetramethyldisiloxane (LL) and maleic anhydride, styrene 0022 [15] or various tertiary phosphines [16,17]. There are also known vinylsiloxane-complexes of palladium [18,19] and rhodium [20,21]. Besides vinylsiloxanes, vinylsilanes have also been used for synthesis of metal p-complexes, e.g., Pt [22,23], Fe [24][25][26][27], Ru [28], Rh [21,[29][30][31][32][33], Co [25,34].…”

Rhodium diamidobenzene complexes: a tale of different substituents on the diamidobenzene ligand

“…Both the Rh–C bond distances of around 2.2 Å and the CC bond lengths of around 1.4 Å correspond to reported values for diolefins coordinated to Rh i . 92,93 The bond lengths between C3–C4 and C5–C6 are elongated by approximately 0.06 Å compared to the iminoquinonoid structure in [3 . MeCN] 2+ (Table 4).…”