4. Overview of RE13≡BiR (E = B, Al, Ga, In, and Tl) systems

R′In≡BiR′ WBI NBO analysis NRT analysis

R′ = Tbt 2.05 σ = 1.78 σ: 0.7626 In (sp0.09) + 0.6469 Bi

92 Recent Progress in Organometallic Chemistry

R′ = Ar\* 2.15 σ = 1.97 σ: 0.7145 In (sp0.07) + 0.6996 Bi

R′ = SiiPrDis2 2.3 σ = 1.92 σ: 0.7341 In (sp53.22) + 0.6790 Bi

R′ = Tbt 2.08 σ = 1.96 σ:0.8268 Tl (sp0.07) + 0.5625 Bi

R′ = Ar\* 2.05 σ = 1.97 σ: 0.8159 Tl (sp0.05) + 0.5782 Bi

(sp99.99)

(sp99.99)

π = 1.94 π:0.4315 In (sp99.99) + 0.9021 Bi (sp99.99)

π = 1.95 π: 0.4788 In (sp99.99) + 0.8779 Bi (sp99.99)

R′ = SiMe (SitBu3)2

(sp50.74)

(sp21.13)

2.21 σ = 1.74 σ: 0.7433 In (sp0.99) + 0.6690 Bi (sp35.62)

(sp0.98)

see Refs. [63, 64], and (2) the natural resonance theory (NRT): see Refs. [73–75].

π = 1.94 π: 0.4230 In (sp99.99) + 0.9061 Bi (sp95.23)

π = 1.94 π: 0.4774 In (sp99.99) + 0.8787Bi (sp99.99)

π = 1.88 π: 0.4468 In (sp42.13) + 0.8696 Bi (sp12.11)

π = 1.78 π: 0.4357 In (sp26.46) + 0.9001 Bi (sp99.99)

compounds that have small substituents, at the B3LYP/LANL2DZ+dp level of theory [1–8, 76–80].

R′Tl≡BiR′ WBI NBO analysis NRT analysis

Notes: (1) The Wiberg bond index (WBI) for the In=Bi bond and occupancy of the corresponding σ and π bonding NBO:

Table 14. Selected results for the natural bond orbital (NBO) and natural resonance theory (NRT) analyses of RʹIn≡BiRʹ

Occupancy Hybridization Polarization Total/covalent/

Occupancy Hybridization Polarization Total/covalent/

ionic

82.11% (Bi)

77.21% (Bi)

80.04% (Bi)

81.01% (Bi)

81.37% (Bi)

77.08% (Bi)

58.15% (In) 2.10/1.15/0.95 In=Bi: 14.33% 41.85% (Bi) In=Bi: 76.37%

17.85% (In) In≡Bi: 0.93%

51.05% (In) 2.11/1.04/1.07 In=Bi: 11.10% 48.95% (Bi) In=Bi: 85.07%

22.79% (In) In≡Bi: 3.83%

55.25% (In) 2.14/1.22/0.92 In=Bi: 14.20% 44.75% (Bi) In=Bi: 81.22%

19.96% (In) In≡Bi: 4.58%

46.11% (In) 1.88/1.27/0.61 In=Bi: 15.31% 53.89% (Bi) In=Bi: 81.02%

18.99% (In) In≡Bi: 3.67%

ionic

68.36% (Tl) 2.15/1.81/0.34 Tl=Bi: 18.71% 31.64% (Bi) Tl = Bi: 71.54%

18.61% (In) Tl≡Bi: 9.75%

66.57% (Tl) 2.11/1.70/0.41 Tl=Bi: 21.11% 33.43% (Bi) Tl = Bi: 70.15%

22.92% (In) Tl≡Bi: 8.74%

Resonance weight

Resonance weight

> This study of the effect of substituents on the possibilities of the existence of triply bonded RE13≡BiR allows the following conclusions to be drawn (Scheme 4):

> 1. The theoretical observations strongly demonstrate that bonding mode (B) is dominant in the triply bonded RE13≡BiR species, since their structures are bent to increase stability, due to electron transfer (denoted by arrows in Figure 1) as well as the relativistic effect [65–68].

$$\begin{aligned} \text{R} & \xleftarrow{\sim 180^{\circ}} \text{Bi} \\ & < 120^{\circ} \\ \text{E}\_{13} &= \text{B, Al, Ga, In, and Tl} \\ \text{R} &= \begin{cases} \text{F, OH, CHs, H, and SiHs} \\ \text{Tlb, Ar\*, SiMe(SiHus)3, and Si/PrDiss} \end{cases} \end{aligned}$$

2. The theoretical evidence shows that both the electronic and the steric effects of substituents are crucial to making the E13≡Bi triple bond synthetically accessible. Based on the present theoretical study, however, these E13≡Bi triple bonds should be weak, not as strong as the traditional C≡C triple bond. From our theoretical study, both bulky and electropositive substituents, such as the silyl groups demonstrated in Scheme 1, have a significant effect on the stability of E13≡Bi triply bonded compounds.
