倉田奨励金研究報告書 第 52 集
2021 年度（第 53 回）助成

自然科学・工学－エネルギー・環境：1 年助成

奨励金№1486

機能集積型金属触媒の創製を基盤とする人工光合成の高度化
鷹谷絢

東京工業大学准教授

Development of Multifunctional Transition Metal
Complexes toward Efficient Transformation ofCarbon Dioxide
Jun Takaya,
Tokyo Institute of Technology, Associate Professor

二酸化炭素のような不活性分子の効率的分子変換反応の開発を目指し、複数の機能を備えた均一系機能集積型金属触媒として、金属－金属結合をもつ異種金属二核錯体の創製と反応性の調査に取り組んだ。その結果、PZnPピンサー型配位子をもつパラジウムならびにルテニウム錯体の合成と構造解析に成功し、これらがルイス酸機能をもつ複合機能遷移金属錯体として働くことを明らかとした。
Aiming at the development of efficient molecular transformation of inert molecules such as carbon dioxide,
synthesis and reactivity of bimetallic complexes with metal-metal bonds were investigated. As a result, we succeeded
in synthesis and structural analyses of palladium and ruthenium complexes having PZnP-pincer-type ligands, which
work as multifunctional transition metal complexes that possess Lewis acidic sites on the ligand.

1．研究内容transformation reactions of carbon dioxide utilizing

Organometallic catalysis employing bimetallic
complexes has emerged as an important strategy insynthetic chemistry. Such bimetallic catalysts are

the multi-functional property of the metal-metalbond.
After several investigations, we have found that

expected to be multi-functional catalysts due tothetheir unique electronic property, coordination

phenylboronate 1a with 0.7 equivalent of ZnMe2 inability, and redox behavior at the metal-metal

toluene at 100°C afforded bis((o-diphenylphosphino)bonds, which are highly promising towardphenyl)zinc 2a in 80％ yield, which was easily

development of efficient transformation reactions ofisolated by reprecipitation of the crude mixture

unreactive molecules such as carbon dioxide.

from THF/hexane (Figure 1). X-ray analysis

However, metal-metal bonds are generally unstabledisclosed that 2a forms a dimer in the cr ystalline

and difficult to make, and efficient synthesis ofstate, where one of phosphorus atoms coordinates tosuch bimetallic complexes and their application inzinc of the other molecule (Figure 2-a). The reaction

synthetic chemistr y have been a great challenge.

was also applicable to (o-dicyclohexylphosphino)

The main purpose in this research is to develop

phenylboronate 1b, affording the corresponding

new hetero bimetallic complexes having a metal-bis((o-dicyclohexylphosphino)phenyl)zinc 2b inmetal

47％ isolated yield, which exists as a monomer inbondthatwouldbeapplicabletotreatmentof(o-diphenylphosphino)

倉田奨励金研究報告書 第 52 集
2021 年度（第 53 回）助成

自然科学・工学－エネルギー・環境：1 年助成

the cr ystalline state (Figure 2-b). Previously, we

pincer ligand and PPh3 as supporting ligands inhave developed the Ru-catalyzed ortho C – H

95％ yield (Figure 3). The 31P NMR showed aborylation reaction of arylphosphines with HBpin

singlet at δ＝44.1 and a broadening peak aroundto afford o-phosphinophenylboronic acid pinacol

δ＝14, which correspond to phosphorous atoms ofesters in high yields. Therefore, these arylboronates

the PZnP-ligand and PPh3, respectively. X-ray

can be prepared easily by Ru-catalyzed C – H

analysis revealed that the geometr y around Pd isborylation of commercially available arylphosphines.

distorted tetrahedral judged from the Zn-Pd-P3

This method realizes the highly efficient, practicalangle (166.21(2)°) and Σ(Pd)＝365.4°, but relatively

synthesis of bis((o-phosphino)phenyl)zinc derivatives

close to square planar compared to the structuresfrom commercially available arylphosphines in twoof phenylene-tethered PBP-Pd complexes (Figuresteps without the use of organolithium reagents.

4-a). The Pd – Zn length (2.6399(5) Å) is almost
comparable to the sum of covalent radii (2.61 Å).
The C1-Zn-C2 angle bends to 149.3(1)° from theoriginal linear structure, which is similar to thevalue of the acridine-ZnPh2 complex (149.0°).

Figure 1

Furthermore, NBO analyses clarified that the Pd –Zn bond consists of donor/acceptor interactions
between an occupied dx2-y2 orbital of Pd and an
unoccupied s-type orbital of Zn, leading to thestabilization energy of 7.5 kcal/mol (Figure 4-b).
These data support that the coordination bondFigure 2. ORTEP drawings of 2a (a) and 2b (b) at
30％ probability level. Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and angles(deg) for 2a: Zn1 – C1＝2.002(3), Zn1 – C2＝2.003(4),Zn1 – P4＝2.478(1), Zn1 – P1＝2.941(1), C1 – Zn1 –C2＝142.2(1); for 2b: Zn1 – C1＝1.9407(16), Zn1 –C2＝1.9407(16), C1 – Zn1 – C2＝180.0.

Figure 3

Having bis(o-phosphinophenyl)zinc derivatives inhand, we examined to use them as PZnP-pincer
type ligands for complexation with varioustransition metals expecting facile formation of
bimetallic complexes having zinc-transition metalbonds. It was found that the reaction of 2a withPd(PPh3)4 in benzene at room temperature
afforded a palladium complex 3a having a PZnP-Figure 4. a) ORTEP drawing of 3a at 30％
probability level. Hydrogen atoms and a solvent
molecule (Et2O) are omitted for clarity. Selectedbond lengths (Å) and angles (deg): Pd – Zn＝2.6399(5),C1 – Zn – C2＝149.3(1). b) NBO analysis on 3a.

倉田奨励金研究報告書 第 52 集
2021 年度（第 53 回）助成

自然科学・工学－エネルギー・環境：1 年助成

exists between a Lewis basic Pd atom and acomplexes were structurally characterized by X-ray

σ-accepting Zn atom with the PZnP-tridentate

analyses using single cr ystals obtained fromstructure. This is the first example of the synthesis

toluene/Et2O for 4a and toluene/pentane for 4bof the phenylene-tethered PZnP-Pd complex that(Figure 6). It is noteworthy that a Et2O moleculebears a neutral, coordinatively unsaturated Zn atom

coordinates on the Zn atom of 4a in the crystalline

as a Z-type metalloligand.

state, proving that the Zn-metalloligand is able toThe versatility of bis(o-phosphinophenyl)zinc 2 asaccept a Lewis basic substrate with keeping thePZnP-pincer type ligands was further demonstrated

Ru – Zn bond. This is highly promising for thein the complexation with Ru(0). A PZnP-ruthenium

synergetic activation of substrates such as carbon

tricarbonyl complex 4a was easily accessible by thedioxide at the M – Zn bond to realize uniquereaction of 2a with 0.33 equiv. of Ru3(CO)12 incarboxylation reactions in synthetic chemistry.

benzene at 100°C (Figure 5). Furthermore, theWe have developed an efficient method toreaction of 2b also proceeded smoothly to give theaccess bis(o-phosphinophenyl)zinc derivatives

PZnP-Ru complex 4b having PCy2 side arms,

via boron-zinc double transmetallation between

demonstrating the high utility of this method too-phosphinophenylboronate and dialkylzinc for theprepare a variety of PZnP-metal complexes. Thesefirst time. This method enables two-step synthesisof phenylene-tethered PZnP-pincer type ligands
from commercially available arylphosphines. The
facile preparation of PZnP-palladium and -ruthenium
complexes is also achieved, demonstrating highversatility of the diarylzinc compounds as isolable
PZnP-pincer type ligands. The structural analyses

Figure 5revealed that the Zn atom works as a Lewis acidic
site, indicating that these Zn-transition metal bonds
are highly promising for cooperative activation andtransformation of unreactive molecules such ascarbon dioxide. This study demonstrates feasibilityof these Zn-Pd and Zn-Ru bimetallic complexes asmulti-functional metal catalysts. Development ofother bimetallic complexes and their application toFigure 6. ORTEP drawing of 4a (b) and 4b (b) at
30％ probability level. Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and angles(deg) for 4a: Ru – Zn＝2.7343(5), Ru – P1＝2.3490(9),Ru – P2＝2.3604(9), Zn – C1＝2.013(3), Zn – C2＝2.012(3), Zn – O＝2.297(3), P1 – Pd – P2＝164.01(3),C1 – Zn – C2＝145.3(1); for 4b: Ru – Zn＝2.697(1),Ru – P1＝2.416(2), Ru – P2＝2.364(3), Zn – C1＝1.990(10), Zn – C2＝1.975(9), P1 – Pd – P2＝153.13(9),C1 – Zn – C2＝152.6(4).

transformation of carbon dioxide are in progress.

2．発表（研究成果の発表）
1）福田一石、原田拓馬、岩澤伸治、鷹谷 絢、ホウ素－亜鉛二重トランスメタル化を利用した
PZnP-ピンサー型配位子の簡便合成と利用、第 68回有機金属化学討論会（オンライン、2022 年）
2）鷹谷 絢、New Aspects of Phosphine-Borane倉田奨励金研究報告書 第 52 集
2021 年度（第 53 回）助成

Frustrated Lewis Pairs、立教大学講演会（オンライン、2021 年）
3）鷹谷 絢、発見のススメ 〜化学研究の楽しみ方〜、第 48 回オルガノメタリックセミナー（触媒化学会、2021 年）
4）鷹谷 絢、New Aspects of Ambiphilic PhosphineBoranes、5 th Inter national Conference on
Organometallics and Catalysis（OM&CAT-5）（オンライン、2022 年）

自然科学・工学－エネルギー・環境：1 年助成