Patai S., Rappoport Z. 1997 The chemistry of functional groups. The chemistry of double-bonded functional groups / 0909 110

17. Syntheses and uses of isotopically labelled compounds

1039

		O	O
O	S	O	O
			S
O			O
					O
	R
	(404)		(405)
	O
		O			O
		S			O
			O	S
		O
		O	O
	(406)		(407)

evolution in this reaction under variable experimental conditions.

1	C CR	2	Ł	R1COCH			R2	C	COŁ
R			C H C OOH !	Ł		2			234a
					13	C or		14	C
				C D

B. Isotope Studies of Chemical Catalytic Reactions

1. The gas-phase reactions of benzene and benzene-D6 with group VIB metal pentacarbonyls and tetracarbonyls

Weak inverse KIEs have been observed in the gas-phase reactions of C6H6 and C6D6 with M(CO)5 (M D Cr and W) and W(CO)4 studied by time-resolved IR spectroscopy486 (equation 235 245).

k1
W(CO)5 C C6H6 ! 2 C6H6 W(CO)5	235

(411)

1040	Mieczysław Ziełinski´ and Marianna Kanska´
	W(CO)5 C C6D6	k2
		! 2 C6D6 W(CO)5	236
	k2/k1 D 1.25 (at 293 K)	(412)

k3

W(CO)5 C CO ! W(CO)6

Cr(CO)5 C C6H6	k4
	! 2 C6H6 Cr(CO)5
k5/k4 D 1.10	(410)

Cr(CO) C D k5 2 C D Cr(CO)

5 C 6 6 ! 6 6 5

k6

Cr(CO)5 C CO ! Cr(CO)6

W(CO) C H k7 2 C H W(CO)

4 C 6 6 ! 6 6 4

		k8
	W(CO)4 C C6D6 ! 2 C6D6 W(CO)4
	k8/k7 D 1.17	k9
	W(CO)4
		C CO ! W(CO)5
	2 C6H6 W(CO)4	k10
		C CO ! 2 C6H6 W(CO)5
		k10/k11 D 1.0805
	2 C6D6 W(CO)4	k11
		C CO ! 2 C6H6 W(CO)5

237

238

239

240

241

242

243

244

245

The gas-phase reaction of nascent M(CO)5 species produced by 355-nm UV laser photolysis of the parent M(CO)6,

h

M(CO)6 ! M(CO)5 C CO

with C6H6 and C6D6, leads to formation of the benzene/M(CO)5 complex in which benzene coordinates to M via an ‘isolated double bond’. The unsaturated species is stable in the millisecond time scale. 2-Coordinated arenes play a central role487 as intermediates in C H bond activation of arene systems.

2. The acid behaviour of zeolites

The catalysis by protonated zeolites, used in industrial cracking, isomerization and alkylation of hydrocarbons, involves proton transfer and formation of carbenium or carbonium ions as reactive intermediates488,489. To understand the function of the zeolite, the reactions between CD4 and acidic hydrogens of OH groups of two zeolite samples have been studied recently490.

3. Deuterium isotope effects in the oxygenate synthesis from CO/H2 on supported [Ru6C]clusters

The syntheses of MeOH, Me2O and HCHO take place in the CO/H2 reaction on the supported carbido-clusters in contrast to the preferential formation of methane and

17. Syntheses and uses of isotopically labelled compounds

1041

hydrocarbons on the conventional Ru catalyst and the supported non-carbido clusters491. CO breathing-induced structural changes upon incorporation or release of carbon monoxide from the [Ru6C] framework has been observed. The large uptake of carbon monoxide (8 11 CO per cluster) on [Ru6C]/MgO and La2O3 prevent the dissociation of CO and increases the selectivity of oxygenate synthesis. Reverse D KIEs (kD/kH in the

range 1.4 2.0, average value of ¾1.7) have been found in the formation of methanol,

D

dimethyl ether and formaldehyde in CO/H2 reactions on [Ru6C]/TiO2, [Ru6C]/La2O3 and [Ru6C]/MgO clusters, respectively. The H2/D2 isotope exchange reaction on [Ru6C]/oxides in CO has been more than 3000 times faster than the steady-state oxygenate synthesis. Therefore, it has been assumed that step (246) is rate-determining in the syntheses of all three oxygenated compounds shown in equation 247. Dimethyl ether is formed by dehydration of methanol on oxide support492. The above conclusion is supported also by calculations491,493 495 of the equilibrium constant for the step shown in equation 246, found to equal KD/KH D 1.9, which coincides with the observed value of 1.7 š 0.3. Inverse D KIEs have been reported493,494 also for reactions on Ru/SiO2 and on Ru/Al2O3.

	CO(a) C H(a) ! CHO(a)		246
			D
Ru	Ru	Ru	Ru
	Ru		D
		D2
	C		Ru
	Ru		C

	Ru	Ru
	Ti2 O		Ti2 O
	d (Ru − Ru) = 0.263 nm		(247)
			CO / D2

				D
	CD3 OD
			O	C
			Ru	Ru
				D
				Ru
	(CD3 )2 O			C
		DCDO
				Ru
			Ru	Ru

Negligible D KIEs in the formation of hydrocarbons (CH4, C2H4, C3H6) which is favoured on contracted [Ru6C]/TiO2 and Al2O3 indicate that the dissociation of CO on the clusters is the RDS. Deuterium isotope shifts in the IR spectra of transient intermediates have been observed in the 1700 1200 cm 1 region. The weak peak at 1576 cm 1 in the CO/H2 reaction corresponding to a formyl species (equation 247) is shifted to 1551 cm 1 after the switch of ambient gas from CO C H2 to CO C D2 at 532 K. The similar deu-

terium peak shifts from 1587 cm 1 to 1545 cm 1 (on Rh/SiO2) and from 1584 cm 1 to 1575 cm 1 (on RuCo3/SiO2) have been observed previously496,497a. The observed deuterium shifts (given in parentheses) in the CO C D2 reaction have been assigned: 3020

1042	Mieczysław Ziełinski´ and Marianna Kanska´

(2260) cm 1 for methane in the gas phase, 2965 (2221) cm 1, 2877 (2186), 1441 (1427) and 1346 (1332) cm 1 to methyl, and peaks at 2929 (2203) and at 2856 (2137) cm 1 to CH of the methylene species. The peak around 1954 cm 1 corresponding to terminal hydride in H2 atmosphere (without CO) at 290 K for [Ru6C]/TiO2] shifted to 1430 cm 1 in D2. The RDS in olein hydroformylation with CO/H2 and CO/D2 has been studied by Yuan and coworkers497b.

4. Deuterium isotope effect in the Pd Cu catalysed carboxylation of alkynes with carbon monoxide

The effect of metal additives [Fe, FeCl2, FeCl3, Co(OAc)2] to palladium(II) catalysing carboxylation of cyclohexane, propane and p-xylene with carbon monoxide have been investigated498 and the highest yields of the corresponding carboxylic acids have been obtained with excess of the mixed catalyst Pd(OAc)2/Cu(OAc)2 (equation 248 250). It has been suggested that the reaction with mixed catalyst proceeds via an electrophilic mechanism similar to that with Pd, but different from the radical mechanism operating in the catalysis by Cu(II) alone and in K2S2O8 system (equation 251).

			CO
			C6H12 ! C6H11COOH		248
			(413)
	C3H8 ! Me2CHCOOH C n-Pr-COOH				249
				Me
p-Me2 C6 H4	CO		Me
		Me		+
			COOH	Me
				Me	(250)
RH C CO C K2S2O8 C 2CF3COOH ! RCOOH C 2KHSO4 C (CF3CO)2					251

This view has been supported by deuterium KIE determinations. Equimolar amounts of cyclohexane and cyclohexane-ŁD12 treated with a Pd(II) Cu(II) mixed catalyst under CO

provided 413 and C6D11COOH in 3.2:1.0 ratio. In a similar reaction catalysed by Pd(II), the ratio was the same. In the reaction catalysed by Cu(II) the above two acids were obtained in equal yields. This indicates that in the carboxylations catalysed by Pd(II) the C H bond cleavage proceeds in the RDS, unlike in the reaction with C(II). In the Pd(II)/Cu(II) system the C H bond is cleaved by palladium. The R PdX (X D CF3COO)-complex reacts fast with CO, palladium(O) is reoxidized with K2S2O8 and the catalytic cycle is completed (equation 252). In the reaction with Cu(II) the radical reaction is predominant. The decomposition of K2S2O8 followed by hydrogen abstraction affords an alkyl radical which, with CO, provides the alkanecarboxylic acid via an acyl radical499,500.

5. Alphaand beta-deuterium isotope effects in the MgX2 and methylaluminoxane promoted intramolecular olefin insertion of Cp2TiCIR complexes

2-Alkyl-6-hepten-1-yl ligands, 414, 415 and 416, deuterium labelled in the ˛- and ˇ-positions, have been synthesized by the method outlined in equation 253 and applied to

17. Syntheses and uses of isotopically labelled compounds

1043

•

•

CF3 COOH

− X

RH

CO

Pd(OAc)2

PdX2

PdX

RPdX

RCPdX

−H •

O

RCOOH + (CF3 CO)2 O

CF3 COOH

RC(O)X

(252)

K2 S2 O8

PdX2

Pd(O)

+ X •

1. NaH, DMF

(EtOOC)2 CHR

(EtOOC)2 C(R)(CH2 )3 CH

CH2

2. 4-bromo-1-pentene

180 °C

H2 O, DMSO, LiCl

1. LDA

CH2

CH(CH2 )3 CD(R)COOEt

2. n-Bu Li

CH2

CH(CH2 )3 C(R)HCOOEt

3. D2 O

LiA H4

1. LiA I D4

(418)

CH2

CH(CH2 )3 CD(R)CH2 OH

2. H2 O

CH2

CH(CH2 )3 CH(R)CD2 OH

(419)

1. LiA I D4

(421)

2. H2 O

CH2

CH(CH2 )3 CD(R)CD2 OH

(420)

CD(R)CH2 Br

4 equ iv.

CD(R)CH2 MgBr

of Mg

419, 420, 421

NBS, P P h3

CD(R)CD2 Br

CD(R)CD2 MgBr

C(R)HCD2 Br

C(R)HCD2 MgBr

Cp 2 TiCl2

CH2

CH(CH2 )3 CD(R)CH2 TiClCp2 (414)

CH2

CH(CH2 )3 CD(R)CD2 TiClCp2 (415)

CH2

CH(CH2 )3 CH(R)CD2 TiClCp2 (416)

R = n-Pr or n-Bu	(253)

study the participation of ˛- and ˇ-hydrogens in the intramolecular insertion of an ˛-olefin into a titanium carbon bond by determining the isotope competitive cyclization rates501. In the MgX2 (X D Cl, Br) promoted cyclization (equation 254) the kH/kD values for the ˛- positions, 416, have been found to be 1.22 š 0.03 and 1.28 š 0.03 for R D n-Pr and n-Bu substrates, respectively. The kH/kD values for the ˇ-position, 414, were 1.09 š 0.02 and 1.10 š 0.02 for these substrates. Cooperative ˛- and ˇ-deuterium isotope effects, 415, for intramolecular olefin insertion, have been 1.36 š 0.03. In the case of insertion

1044	Mieczysław Ziełinski´ and Marianna Kanska´

Pr-n

Cp2 XTi

HCl

Pr-n

Me

X X X

X M M

X X

D R

Cp Ti

2 +

D D

(422)

	Pr-n		Bu-n
	Cp2 XTi	Cp2 XTi
MgX2 or MA O		+
	HCl	HCl	MgX2 or MA O
Pr-n	Bu-n		Bu-n

(254)

Me

Me

Cp2 XTi

HCl

Bu-n

			Me
X	X	X	X X		X
X M	M		X M	M
	X		X
	D	R		D	D
Cp Ti			Cp	Ti
2	+		2	+	R
	D	D		D

	(423)			(424)
	X X			X
X M		M	M
	X		D	X
Cp	Ti			D
2	+	D		R

(425)

17. Syntheses and uses of isotopically labelled compounds

1045

promoted by methylaluminoxane (MAO) an inverse D KIE has been observed for ˛- hydrogen (kH/kD D 0.88 š 0.09) for the n-propyl and kH/kD D 0.95 š 0.04 for the n-butyl substrates, respectively), but the kH/kD value of 1.06 š 0.04 has been observed for ˇ-hydrogen participation for each substrate (414).

The above findings are evidence for the ˛-H participation and slight ˇ-H participation in the RDS of ˛-olefin insertion for titanium-based Ziegler Natta systems and for any system which models a propagating ˛-olefin polymer chain. Smaller values of ˇ-D KIE than of ˛-D KIE are observed because coordination of the hydridic ˇ-H in an agostic interaction does not require the same degree of geometric change at the ˇ-C as is necessary in the case of agostic interaction of the ˛-carbon (structures 422, 423, 424 and 425 in equation 255).

Me	D	O	D	O
Cp	Al
			Al
Y
	Cα
X				Dβ (equatorial)
Ti	R3	Cβ
Cp			R1	CH2
	H
			(axial)
				R4
				H
	(426) Y =	Cp2 TiCl		R2
				(255)
	D		D
Me		O		O
Cp	Al
			Al
				Me
Y	Cα
X			D
Ti	R3	Cβ
Cp			R1	CH2
	H
				R4
				H
(427) isotactic product				R2

The temperature-dependent stereoregular MAO-promoted polymerization of ˛- olefins502 has been explained by ˇ-hydrogen interactions in the olefin insertion and formation of a six-membered C˛ Cˇ Dˇ Al O Al ring TS. The stereoselective isotactic product formation occurs as a result of the substituent orientation at the ˇ-carbon (R1 vs CH2CHR2R4 in the conformationally restricted 426; equation 255).

6. Deuterium study of the mechanism of oxidation of tungsten 1 -2,5-dihydrofur-3-yl compounds to 1- 3-butenolide derivatives

The deuterium-labelled 428 has been synthesized503 via PhC CCD2OH to confirm the source of the Cˇ H hydrogen in 429. The 1H-NMR spectra of the furan, derived from

1046	Mieczysław Ziełinski´ and Marianna Kanska´

428, confirmed a 1,2-hydrogen shift (equation 256).

O

CHMe2

D2 C

WCD2 C

CPh + Me2 CHCHO

BF3 .ET2 O

W

Ph

Ph3 CBF4

(428)

O

CHMe2

O

W

α

MCPBA / hexane

W

α

CHMe2

β

O

β

(256)

NaOA c / HOA c

Ph

Ph

H

H

(429)

O

α

O

CHMe2

W

β

Ph

H

W = CpW(CO)3; H = D or H

7. Deuterium isotope effects in the oxidative cleavage of unsaturated acids by quinolinium dichromate

A small inverse KIE, kH/kD D 0.78, has been observed504 in the oxidation of cinnamic- ˛-d acid, 430 with quinolinium dichromate (QDC) (equation 257). In the case of the oxidation of ˇ-d-cinnamic acid, kH/kD D 0.987 at 40 °C.

					O
3 PhCH		CDCOOH + 4 Cr(VI) + 6 H2 O	DMF	3 RCHO + 3DCCOOH + 4 Cr(III) + 12 H+
(430)				ρ = − 4.0	(257)

The above values of ˛- and ˇ-D KIEs indicate a change in the state of hybridization from sp2 to sp3 of the ˛-carbon atom and no sp2 character of hybridization change at ˇ-C in the RDS of the oxidation of 430 by QDC. A substantial C˛ O bond formation and negligible Cˇ O bond formation take place in TS after QDC attack. The mechanism of reaction 257 involves electrophilic attack of the protonated oxidant on the double bond of the substrate 430, formation of the carbonium ion, 431, its reaction with water to form the intermediate 432, conversion of 432 to the chromate ester 433 and its cleavage to products (equation 258). The positive value ( H# D 82 kJ mol 1) of enthalpy and negative value of entropy ( S# D 57 kJ 1 mol 1) of the reaction indicate that the TS of reaction is highly solvated and considerably rigid.

8. The rearrangement of 3-phenyl propene-3,3-D2 435 catalysed by [Ru(H2O)6] 2C

The rearrangement of 435 by [Ru(H2O)6]2C , 434, in C2D5OD, (CD3)2 CO, THF- D8, and Et2O provided505 a mixture of trans-phenylpropene with deuterium content in

17. Syntheses and uses of isotopically labelled compounds

1047

all carbons of the propyl chain, i.e. 436-D1 and 436-D2 (equation 259). The ratio of 436-D1 to 436-D2 is insensitive to solvent. The three IR signals in the region of the C D stretching vibration (2236, 2195 and 2160 cm 1) agree with deuterium on all three carbons of the propene chain. The rearrangement of 435 to 436 was irreversible. 79% of 436. PCHŁ DCHŁ CH3Ł , contained 1 deuterium atom and 19% of 436 contained two deuterium atoms (determined by 1H NMR and 13C NMR) (equation 260).

+

O

OH

PhCH

CDCOOH

PhCH

CDCOOH

H2 O

PhCH

CDCOOH +

Cr

O

HO

O

+

− H +

O

OQH

(430)

O

Cr

OH

HO

Cr

OH

OQH+

OQH+

(431)

(432)

(258)

Ph

COOH

CD

O

O

H2 O

QDC

PhCHO + DCCOOH + Cr(III)

Cr

HO

OH

O

OQH

+

(433)

D

1

CH3

(436) - D1

Ph

3

2

D

PhC

D C

H

C

H

[Ru(H2 O)6 ]2 +

CH2 D (436) - D2

(3 )

(2 )

(1)

(434)

2

2

Ph

(435)

D

Ph

CH3

(436) - D2

D

(259)

The above results are consistent with a steric specific syn 1,2-addition elimination of metal hydride intermediate which is formed fast in a pre-equilibrium f[MH] × [MD]g and adds to the olefinic substrate to form the metal alkyl intermediate (equation 261). The ˇ-hydride elimination of the most stable rotamer (equation 262) is the RDS in the rearrangement, leading to a metal hydride product complex, which starts a new cycle faster than uncoordinated metal hydride. The protonated catalyst, 434, produces a precursor

1048	Mieczysław Ziełinski´ and Marianna Kanska´

of the type [(H2O)5Ru( 2-olefin)]2C which rapidly yields the ruthenium alkyl complex. The deuterium exchange between metal hydride and solvent has been found to be slow compared to rearrangement.

			+ MH (70 %)
PhCD2 CH		CH2		PhCD2 CHCH3
435 - D2			− MH
				M

(260)

+ MH

−MH

− MD

30 %

PhCD2 CH2 CH2 M

PhCD

CHCH3

+ MD

PhCD

CHCH2 D

MH

RuH

− MD

+ MH

+ MD

− MD

435 - D2

PhCD2 CH

CHD

+ MD

− MH

+ MH

PhCD2 CD

CH2

PhCD

CDCH3

− MH

− MD

(261)

H

H

Me

Me C

C

R

− MH

M

H

R

M

H

H

C

C

R

(262)

Me

H

Me

H

R

M

C

C

R

− MH

H

H

Me

At

302 K,

the

435-D2 (after

an

induction

period of 5 min)

rearranges 2.3 times

lower than undeuteriated 435. This DKIE has not been interpreted in terms of TS structures 437 434 probably due to the lack of data concerning the rearrangement of PhCD2CDDCD2, PhCD2CDDCH2 and PhCH2CHDCD2 isotopomers506.

D

D

R

RCD2

CHD

RCD2

C

D

Ru

Ru

H

H

Ru

(437)

(438)

(439)