Lanthanide and Actinide Chemistry and Spectroscopy - American

4 Synthesis and Spectroscopy of Novel Mixed-Ligand Organolanthanide Complexes

Downloaded by SUNY STONY BROOK on October 15, 2014 | http://pubs.acs.org Publication Date: September 23, 1980 | doi: 10.1021/bk-1980-0131.ch004

R. DIETER FISCHER and GUDRUN BIELANG Institut für Anorganische und Angewandte Chemie der Universität Hamburg, D-2000 Hamburg 13, Germany

In the past few y e a r s , c o n s i d e r a b l e development has taken p l a c e in the field of f-element o r g a n o m e t a l l i c s ( 1 , 2, 3), h i g h l y r e p r e s e n t a t i v e examples c i t e d being u s u a l l y complexes i n v o l v i n g one s i n g u l a r l i g a n d ("homoleptic" o r g a n o m e t a l l i c s ) , e.g. ( C H ) f M w i t h n = 2-4, [ ( C H ) 2 f M ] q (q = 0 or -1), [Li(tmed)] [Ln(CH3)6] (4) and [(CH )2P(CH2)2]3 M (5). Although e x t e n s i v e s t u d i e s of such compounds undoubtedly have t h e i r m e r i t s apart from p u r e l y a e s t h e t i c aspects, it is almost e x c l u s i v e l y the much wider field o f mixed-ligand systems that provides v a l u a b l e i n f o r m a t i o n wherever chemistry w i t h f - o r g a n o m e t a l l i c s is concerned. Thus it is well-documented t h a t v a r i o u s organouranium compounds can c a t a l y z e the s t e r e o s p e c i f i c formation of cis-1,4polybutadienes from 1,3-butadiene (6) in which homogeneous p r o cess complexes w i t h organic l i g a n d s are h i g h l y s u p e r i o r t o classical oxides or h a l i d e s . Although w e l l - d e f i n e d organo-uranium complexes such as (C5H5)3UX and ( C 3 H 5 ) U/Lewis a c i d , r e s p e c t i v e l y , have been reported t o be most efficient, the (unknown) catalytically a c t i v e species will undoubtedly be a mixed-ligand system i n v o l v i n g the s u b s t r a t e as well as a c o - c a t a l y s t and/or the solvent. We can v i s u a l i s e the c a p a b i l i t y o f s u i t a b l e lanthanide (Ln) compounds (J_, 6 ) , e.g. as homogeneous c a t a l y s t s w i t h respect t o o l e f i n s , by i n v o k i n g s i m i l a r i n t e r m e d i a t e s . Although the s e r i e s of r e p o r t e d l y c a t a l y t i c a l l y a c t i v e Ln-complexes spans from the pure t r i h a l i d e v i a t r i s ( B - d i k e t o n a t o ) c o m p l e x e s t o the organom e t a l l i c t r i s ( c y c l o p e n t a d i e n y l ) and t e t r a ( a l l y l ) c o m p l e x e s ( 8 ) , r e s p e c t i v e l y , no r e a l l y o p t i m a l combination of l i g a n d s on a L n element has been found so f a r . Promising aspects a r e , however, based on some evidence f o r " r e a c t i o n s t e e r i n g " i n that e i t h e r c i s - or trans-polybutadienes can be obtained from 1 , 3 - d i e n e s , and e i t h e r polymers or metathesis products from monoolefins, r e s p e c t i v e l y (Table I ) . 5

5

n

8

8

f

3

3

4

0-8412-0568-X/80/47-131-059$05.25/0 © 1980 American Chemical Society

In Lanthanide and Actinide Chemistry and Spectroscopy; Edelstein, N.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

60

LANTHANIDE AND ACTINIDE CHEMISTRY AND SPECTROSCOPY

Table I. C a t a l y t i c A c t i v i t y of Lanthanide Compounds towards Unsaturated Hydrocarbons (according to References I> 1, 7, 8) Starting

Substrate

Product(s)

monoolefin

olefin-metathesis saturated polymers cis-1,4-polymers

"Catalyst"

SmCl /AlEtCl LnCl /AlEt Ce-octanoate/AlR Ln(diket) /A1R (C H ) Sm LnCl /Sn(allyl) /4LiR L i [ L n ( a l l y l ) i+] -dioxane (C H )3Sm 3

2

3

f? tt

3

3

3

5

5


trans-1,4-polymer

1,3-diene

3

3

5

ii

3

II

it it

h

HCCC H

5

6

it t r iphenylb enz ene

5

General Reaction P a t t e r n Frequently, the p r e p a r a t i o n of a d i s t i n c t mixed-ligand complex, L MX ( L = l i g a n d bonded v i a M-C bonds), i s q u i t e a d i f f i c u l t task, i n p a r t i c u l a r i f the s t a r t i n g m a t e r i a l i n v o l v e s a pure metal h a l i d e . In organolanthanide chemistry, however, an almost unique and very e f f e c t i v e route to a r r i v e at a l a r g e v a r i e t y of C p L n X systems (Cp = r^-CsHs) i s o f f e r e d by eq. (1) c

c

m

n

m

f

aC

C p M + mH -X

->

n

f

Cp _ MX n

m

m

+ mC H 5

(1)

6

5

The stepwise s u b s t i t u t i o n of r) -coordinated Cp-ligands i n i t i a t e d by the attack of a proton a c i d i c reagent H -X i s u s u a l l y p o s s i b l e under m i l d c o n d i t i o n s i n v a r i o u s i n e r t organic s o l v e n t s , and the r e s u l t i n g cyclopentadiene i s e a s i l y removable with the s o l v e n t . Reaction (1) was f i r s t adopted by F i s c h e r and F i s c h e r i n 1965 (10), and has been extended mainly by Kanellakopulos et a l . (11, ac

J2). U n l i k e the lanthanide complexes Cp Ln, and many degradation products, C p _ L n X , some a c t i n i d e , and the m a j o r i t y of d-block metal, cyclopentadienides are not s u s c e p t i b l e to r e a c t i o n (1). A reasonably good t e s t f o r the r e a c t i v i t y of metal-bonded Cp with H-acids c o n s i s t s i n the a d d i t i o n of water or methanol. While a l l known lanthanide complexes w i l l immediately be decomposed, many organo-uranium compounds of the type Cp UX e i t h e r simply add H 0 and/or undergo s u b s t i t u t i o n of X (13): 3

3

n

n

3

2

H0 2

Cp UX 3

+

H0

[Cp UX(H 0)]

2

3

(2)

2

H0 2

[Cp UX(H 0)] 3

2

[Cp U(H 0) ] 3

2

x

+

X


(3)

4.

FISCHER AND BIELANG

Mixed-Ligand

Organolanthanide

Complexes

61

+

While aqueous s o l u t i o n s o f the c a t i o n [Cp3U(H20) ] remain s t a b l e down t o a pH of -1, the presence of f l u o r i d e ions causes the immed i a t e rupture of a l l Cp-U bonds ( 9 ) . Likewise, B-diketones have been reported t o replace one Cp-ligand (and the h a l i d e ) from Cp UCl (J8). Kanellakopulos et a l . have demonstrated the wide a p p l i c a b i l i t y of the p r o t i c a c i d N H f o r the elegant p r e p a r a t i o n of many mixed-ligand metal cyclopentadienides of f-block and main group elements (14): x

3

+

4

THF Cp M + mNH^X — — y Cp MX *n reflux *n-m m

+ mCpH + mNH


(4)

3

H

p

ac

If the a c i d H -X i s a l s o f u r n i s h e d with a lone e l e c t r o n p a i r , the f o l l o w i n g two-step mechanism appears f e a s i b l e i n case o f s t r o n g l y L e w i s - a c i d i c substrates such as C p % : 3

Cp

f 3

M

+

f flp C p M^-X-H

:X-H

f

Cp M«-X-H

aC

f

-> l / 2 [ C p M X ]

3

(5a)

3

2

+ CpH

2

(5b)

aC

U s u a l l y , the adduct Cp %+-XH o f f e r s favourable s t e r i c c o n d i t i o n s f o r a subsequent i n t r a m o l e c u l a r H-transfer t o one of the C p - l i gands. Moreover, the proton a c i d i t y of HX w i l l o f t e n increase by the c o o r d i n a t i o n . Thus, pure Cpi+U which i s s u r p r i s i n g l y s t a b l e against water has no p o s s i b i l i t y to form an adduct with H2O, while the shape of the Lewis base HCN would not completely preclude t h i s p o s s i b i l i t y . Anhydrous HCN replaces i n f a c t one CpH-molecule (14). Following the pathway of eqns. (5a) and (5b), even a " p r o t i c a c i d " as weak as NH has s u c c e s s f u l l y been a p p l i e d t o replace CpH 0 0 ) 3

3

U

Cp Yb

q

U

3

2

NH3

' ->Cp Yb-NH 3

(green)

3

!c H

C >

l/2[Cp YbNH ]2

p

2

( l i g h t green)

2

(6)

(bright yellow)

Reaction (6) thus e x e m p l i f i e s , i n a sense, t h e ' r e v e r s a l of the well-documented s u b s t i t u t i o n of secondary amines by CpH (15), U(NR K 2

+

2CpH

-> C p U ( N R ) 2

2

2

+

2HNR

2

(7)

There are v a r i o u s , a l b e i t mainly unpublished, observations sugg e s t i n g that many organic amines, phosphines, and other Lewis bases c a r r y i n g at l e a s t one H-atom w i l l i n i t i a t e r e a c t i o n (6), however, without y i e l d i n g i s o l a b l e adducts (16, 17). P o t e n t i a l Proton Acids of S p e c i a l I n t e r e s t For a b e t t e r understanding, and f u r t h e r e x p l o r a t i o n of the


62

LANTHANIDE AND ACTINIDE CHEMISTRY A N D SPECTROSCOPY

general a p p l i c a b i l i t y , of r e a c t i o n (1), a l a r g e r , and more s y s t e matic, v a r i a t i o n of the p r o t i c a c i d H-X than p r e v i o u s l y has appeared worthwhile. Table I I . Survey of Proton Acids H-X Subjected t o Eq. (1) SC


Reagent H -X

approximate p K

carboxylic acids B-diketones and B-ketoimines pyrazole cyclopentadiene p y r r o l e and i t s benzo-derivatives indene phenylacetylene and other alkynes HCCR fluorene (ammonia) (toluene)

a

ca. 5 ca. 9 14 15 - 16 16,5 20-21 20-21 25 33 37 - 39

Table I I o f f e r s a survey of the c l a s s e s of compounds, and s p e c i f i c s i n g u l a r compounds, r e s p e c t i v e l y , that have so f a r been subj e c t e d t o r e a c t i o n s as s p e c i f i e d by eq. (1). Two main o b j e c t i v e s governing t h i s s e l e c t i o n have been (a) the question on the r e l e vance of the proton a c i d i t y of the reagent H-X, and (b) our i n c r e a s i n g i n t e r e s t i n the p r o p e r t i e s of mixed-ligand systems C p L n X (n+m = 3) where X i s another polydentate l i g a n d . While u n t i l r e c e n t l y no example of such a complex with a genuine chel a t e l i g a n d was known, there i s , moreover, p a r t i c u l a r i n t e r e s t i n r e a c t i o n (1) as a p o s s i b l e route t o complexes of the type [ C p L n X ] of the l i g h t e r Ln-elements (Ce-Sm) . This sub-class of organolanthanides has been found t o be very unstable (19) the only well-documented example being the product of the r e a c t i o n of Cp Nd with HCN, [Cp NdCN] (12). T h i s complex i s probably o l i gomeric and s t a b i l i z e d by b r i d g i n g CN-ligands. In t h i s context, the a c t i n i d e complex [ C p U C l ] obtained from Cp3U and anhydrous HC1 (20) may be considered as an outstanding example of a nono l i g o m e r i c Cp ^MX-system where e x h i b i t s an i o n i c radius comparable t o those of the e a r l y L n - i o n s . The pK -values of the a c i d i c reagents i n t a b l e I I vary over more than f i v e u n i t s . I t should, however, be kept i n mind that the determination of pKvalues i n non-aqueous media, and t h e i r t r a n s f e r a b i l i t y from one medium t o another, present r a t h e r d e l i c a t e problems (21). Other important f a c t o r s to account f o r i n view of the r e a c t i v i t y o f an i n d i v i d u a l H -X system are: (a) i t s i n i t i a l Lewis b a s i c i t y , (b) the a c t u a l increase i n proton a c i d i t y on c o o r d i n a t i o n , (c) the t o t a l " h a p t i c i t y " f i n a l l y d i s p l a y e d by X, and (d) v a r i o u s essent i a l steric conditions. n

m

2

n

3

2

n

2

n

2

3 +

a

ac


4.

FISCHER AND BIELANG

Mixed-Ligand

Organolanthanide

Complexes

63

Table I I presents examples of reagents that i n v o l v e 0 and N as w e l l as C as the proton-donating element. Only very few compounds from the t a b l e such as formic a c i d (19), ammonia (10), and phenylethyne (22) had been reacted with Cpa^M p r i o r to our study; i t has been claimed that Cp3Sm only c a t a l y z e s the t r i m e r i z a t i o n of phenylethyne.


C h a r a c t e r i z a t i o n of Reaction Products For the m a j o r i t y of r e a c t i o n s i n v o l v i n g a "heavier" L n - e l e ment Yb was p r e f e r r e d , owing to the r e l a t i v e l y good s o l u b i l i t y o f Cp3Yb even i n toluene and pentane, and t o the very c h a r a c t e r i s t i c colour change (see eq. 6) whenever a r e a c t i o n of type (1) i s taking p l a c e . More d e t a i l e d i n f o r m a t i o n on the nature of an organo-ytterbium system i n v o l v i n g Cp-ligands i s o f f e r e d by the o p t i c a l abs o r p t i o n s p e c t r a . The s p e c i f i c d i f f e r e n c e s of f - f - s p e c t r a of Yb -complexes of the types Cp3Yb, Cp2YbX and CpYbX2 have been discussed e a r l i e r (16, 23). Y b - c y c l o p e n t a d i e n y l complexes o f f e r the a d d i t i o n a l advantage that the l o w e s t - l y i n g charge t r a n s f e r corresponding t o the i n t r a m o l e c u l a r redox process (23): [ligands] 4f • [ligands]" 4f may l i e as low as c a . 16.600 c m i f three n - C p - l i g a n d s - o r e v e n t u a l l y a corresponding set of s u f f i c i e n t l y reducing ligands - are i n v o l v e d . I t has a l s o turned out mainly during our s t u d i e s of mixedl i g a n d organo-ytterbium systems that many Yb -complexes present e x c e l l e n t c o n d i t i o n s f o r the observation of t h e i r H-NMR s p e c t r a i n s p i t e of the strong paramagnetism of t h i s f - s y s t e m . P r e v i o u s papers d e a l i n g p a r t i c u l a r l y with P r - and U -systems, respect i v e l y , have already pointed out the almost i n d i s p e n s a b l e r o l e of the NMR s p e c t r a of l i g a n d s bonded to paramagnetic % - c e n t r a l ions (24, 2 5 ) . Table I I I e x e m p l i f i e s by some room temperature Cp-proton s h i f t data o f Yb -complexes the high d i a g n o s t i c value even of one s i n g u l a r NMR s h i f t value per system. More s o p h i s t i c a t e d s t u d i e s are concerned with the complete temperature dependence of p a r t i c u l a r resonances over a range of u s u a l l y 100 degrees (-70 to + 30 °C). F i g u r e 1 presents as an example the ^-NMR-spectra of two d i f f e r e n t Y b - o r g a n o m e t a l l i e s , [ C p Y b 0 C ( n - C H ) ] and [Cp YbC (n-CttH9)] 3, r e s p e c t i v e l y , both o f which c o n t a i n two Cpligands and one t e r t - b u t y l group i n the secondary l i g a n d . A l though the s p e c t r a l patterns regarding the numbers, and r e l a t i v e i n t e n s i t i e s , of the resonances are compatible, the q u i t e dramat i c a l l y d i f f e r e n t i s o t r o p i c s h i f t s s t r o n g l y suggest d i f f e r e n t e l e c t r o n i c and/or s t e r i c c o n d i t i o n s i n the two s p e c i e s . Figure 2 e x e m p l i f i e s the v a r i a t i o n o f the " i s o t r o p i c " proton s h i f t s of the Y b - a l k y n y l complex with the temperature. I t i s noteworthy that the s h i f t of the a-CH protons of the t e r t - b u t y l 3+

3+

1

-1

1 1 +

5

3+

13

3 +

l++

3+

3+

2

2

2

4

9

2

2

3 +

2


64


Table I I I . Cp-ring ^-NMR s h i f t s of v a r i o u s systems [ C p Y b X ] . ( a ) : reference s i g n a l : i n t e r n a l TMS; ( b ) : i n parentheses: weaker s a t e l l i t e resonances; ( c ) : weak "shoulder" present; (d): probably formation of 1:1 adduct; (e): CH COCHC(CH )N0. 2

n

3


3

Ligand X

Solvent L

n -c H

toluene-ds

5

5

5

-55,2 -54,4

it

it CI

2

CI

2

(-31,9) -34,0 -35,0 (-29,3) -36,5 (-33,0) -38,0

THF-ds benzene-d6 toluene-ds

-10,0 -12,0 -19,0 -33,9

3

NH

2

II

n-Ci H C0 "ketim"e t

9

2

n—C 14.H9C 2

11

C HnC FcC 6

2

b

11

toluene-d6

tt tt tt

2

2

-57,6 -31,4 -56,6

3

3

d

probably monomeric adducts Cp YbCl-nL 2

a l l dimeric

(-64,2) (-48,9.. -60,0) (-59,6) -56,3^

r e f e r e n c e s i g n a l : i n t e r n a l TMS i n parentheses: weaker s a t e l l i t e weak "shoulder" present probably formation of 1:1 adduct CH COCHC(CH )N0

P0

probably a l l dimeric

CD CN THF-ds (CD ) CO pyridine-ds 3

It II If

Remarks

with

-61,0 -61,6 -65,6

benzene-d6 toluene-d6 CD C1

II II

a: b: c: d: e:

Cp^H-NMR S h i f t (s)

t r i m e r i c (CeHe) with p y r i d i n e - d

resonances

3



• 100

8

• 80

• 60

• AO

J • 20

CH,

c

2

" VH 2

2

Jt

9

2

-20

-AO

-60

Cp

2

2

Figure 1. Room temperature *H-NMR spectra of (a) [Cp Yb0 C(n-C H )] and (b) [Cp YbC (n-CifloJJs in toluene-d solution. Internal standard: TMS; the magnetic field increases towards negative shifts.

• 120

9

a-CH

CH

y~ 2

P-CH 2

W**J

(a)

9

a-cH

p

CH,

Cp


66


group i s almost comparable i n magnitude w i t h the a-CH s h i f t o f 2

2

the

5 f - s y s t e m CpsUCn-CitHg) ( 2 6 ) .

None o f the " l i g h t e r " Ln-elements o f f e r s optimal c o n d i t i o n s f o r the f a c i l e v i s u a l i n d i c a t i o n o f a s u c c e s s f u l r e a c t i o n o f Cp Ln w i t h H -X. Moreover, the low s o l u b i l i t y o f both the s t a r t i n g m a t e r i a l Cp3Ln (Ln = Pr, Nd, Sm) and o f most r e a c t i o n products a f f o r d s d e a l i n g w i t h suspensions r a t h e r than w i t h v e r i t a b l e s o l u t i o n s . As, moreover, the i s o t r o p i c H-NMR s h i f t s o f Cp Nd/Lewis base adducts are e x c e p t i o n a l l y weak (25), the best s p e c t r o s c o p i c method t o i d e n t i f y , and c h a r a c t e r i z e , most N d organometallics i s a b s o r p t i o n spectroscopy ( e i t h e r o f s o l u t i o n s or of Teflon p e l l e t s ) i n the NIR/VIS range. The r e g i o n o f the s o - c a l l e d h y p e r s e n s i t i v e t r a n s i t i o n s between c r y s t a l f i e l d s t a t e s of the manifolds ^19/2 (ground manifold) and Gs/2 (ca. 580 610 nm) has proved t o be of p a r t i c u l a r l y high d i a g n o s t i c v a l u e . Even a t room temperature, and i n case o f p o l y c r y s t a l l i n e s o l i d samples ( i . e . p e l l e t s ) , v a r i o u s ensembles of f a i r l y sharp f - f t r a n s i t i o n s appear which a l l o w t r a c i n g the c o n s t i t u e n t s o f mixtures o f compound even i n cases o f r a p i d i n t e r c o n v e r s i o n . Figure 3 gives an impression o f the appearance o f some t y p i c a l spectra o f Nd -complexes i n the " h y p e r s e n s i t i v e r e g i o n " . The o p t i c a l s p e c t r a o f organometallic P r - s y s t e m s u s u a l l y s u f f e r from the l a c k o f s u i t a b l y h y p e r s e n s i t i v e t r a n s i t i o n s as w e l l as from the w i d e l y expanding s i d e wing o f a charge-transfer band. On the other hand, theH-NMR spectra of the few s u f f i c i e n t l y s o l u b l e P r - c o m p l e x e s so f a r obtained have turned out too complex t o a r r i v e a t r e l i a b l e assessments. ac

3

1

3


3 +

k

3+

3+

1

3+

R e s u l t s and D i s c u s s i o n ac

S i g n i f i c a n c e o f the pK -Value of H -X. The t o t a l o f r e s u l t s obtained i n t h i s study suggests that a l l reagents H -X w i t h p K - v a l u e s lower than that o f cyclopentadiene are capable of r e a d i l y r e p l a c i n g more than one, and most f r e q u e n t l y a l l , Cpl i g a n d s of the substrate Cp Ln. Thus i t i s only by dropwise a d d i t i o n o f the s t o i c h i o m e t r i c q u a n t i t y o f the reagent that an immediate s u b s t i t u t i o n o f a l l Cp-ligands can be avoided. Exemp l a r i c products o f such c a r e f u l t i t r a t i o n - l i k e procedures have been the before-mentioned U(III)-complex [Cp2UCl] (20), the monovaleriato complex [Cp2Yb02C(n-CitH9)] 2 (27) , various" systems i n v o l v i n g d e r i v a t i v e s o f B-diketones, [Cp2^n(chel)] (see below), and even the (probably o l i g o m e r i c ) r e a c t i o n product (1:1) o f Cp3Yb and pyrazole ( p K ^ 14,2). Reaction o f Cp Ln w i t h an excess o f " s t r o n g l y a c i d i c " (pK < 15) reagents u s u a l l y leads t o the non-organometallic products L n X . The l i g h t brown t r i s ( p y r a z o l y l ) complex of Yb which i s again very i n s o l u b l e even i n THF i s o f i n t e r e s t i n view o f the nature o f the p y r a z o l y l anion as a v e r s a t i l e polydentate l i g a n d . By a p p l i c a t i o n o f an excess o f the B-ketoimine C H 3 C O C H C ( C H 3 ) C N H R = "H-ketim" (see below) on Cp3Ln, the corresponding t r i s ( c h e l a t e ) a

ac

a

3

n

n

a

3

a

3


4.

FISCHER AND BIELANG

Mixed-Ligand

ppm

Organolanthanide

Complexes

67

CL-CH

2

200150-

2

-CH

2

Y

100-

CH,

50-


3-CH

o-

[-10-3]

-50-100 Cp 2

Figure 2. Variation of the H-NMR shift values of [Cp YbC (n-Ci H )]3 temperature 2

2

t

9

with

Figure 3. Absorption spectra (toluene solution, room temperature) of (a) Cp Nd and (b) "Cp Nd(thd)" in the region of hypersensitive transitions (thd = 2,2',6,6'-tetramethylheptane-3,5-dionate) 3

2

570

580

590

600

610

[nm]


68

LANTHANIDE AND ACTINIDE CHEMISTRY AND

SPECTROSCOPY

complexes L n ( k e t i m ) 3 are r e a d i l y a c c e s s i b l e . I t i s worth ment i o n i n g i n t h i s context that the f i r s t " c l a s s i c a l " lanthanide complex i n v o l v i n g the c h e l a t e l i g a n d s ketim (R = C6H5 and t-Ct+Hg) have not been d e s c r i b e d u n t i l 1979 (28), e.g. Ln(0-iC H )3 3

7

+

C6H6

n H-ketim

reflux

(8)

(iC H 0) _ Ln(ketim)


3

7

3

n

n

+ n i-C H OH 3

7

So f a r , however, i t has not been p o s s i b l e to a r r i v e at t r i s (ketimino)complexes by t h i s route. Somewhat s u r p r i s i n g l y , Cp3Ln-systems may a l s o r e a c t with a wide v a r i e t y of reagents i n cases of c o n s i d e r a b l y l a r g e r pK values than that of cyclopentadiene (pKa > 15). One important d i f f e r e n c e i s , however, that the "weaker a c i d s " r e p l a c e no more than one Cp-ligand per metal complex. In some i n s t a n c e s , such a r e a c t i o n i s notably improved by r e a c t i n g the Cp3Lnsystems with the s o l v e n t - f r e e H-X at e l e v a t e d temperatures up to 60 °C. For example, r e a c t i o n of Cp3Yb even with p y r r o l e (pyr-H) (pK - 16,5) only y i e l d s the orange product [ C p Y b ( p y r ) ] the o p t i c a l s p e c t r a of which are devoid of evidence f o r a r\ -coord i n a t i o n of the p y r r o l y l l i g a n d . Somewhat d i f f e r e n t metal-top y r r o l y l bonding c o n d i t i o n s may be expected f o r the deeply green t r i s ( p y r r o l y l ) lanthanide complexes which are a c c e s s i b l e according to eq. 9 (29). F i g u r e 6 shows the NIR/VIS-spectrum of Yb(pyr) . a

a

2

n

3

LnCl

3

+ 3Na(pyr)

toluene or THF • r e f l u x , l h , room temp. 170

green s o l n .

°C

decomp. Ln(pyr)3 colourless soln.

(9)

EtOH Ln = Sm: Ho: Yb:

brownish-green dark green almost b l a c k

Reaction w i t h fi-Diketones. U n l i k e with the other "strong a c i d s " H -X mentioned above, the f i n a l products of v i r t u a l l y s t o i c h i o m e t r i c r e a c t i o n s (1:1) of Cp Ln (Ln = Yb, Ho, Sm, Nd and Pr) with the B-diketones ac

3

R H-diket

hc: ^c-o*

H

R

=

CH , t—C1+H9 3

(10)

R


4. FISCHER AND BIELANG

Mixed-Ligand

Organolanthanide

2 CpLn(chel) ^ ^ [Cp2Ln(chel)] ^ 2

oligomers

2

oligomers

y[CpLn(chel)] • Cp3Ln 2

2

111)

CpLn(chel)

2

yCpLn(chel) +-jLn(chel) 2


Complexes

3

^. ^ oligomers

chel = diket, ketim Scheme 1

"Nd

Nd

Figure 4. Schematic of [Cp Nd(ketim)] in case of one particular phase of unsymmetric coordination 2

0

'"^

(a)

Figure 5. Optical absorption spectra of (a) Cp Nd and (b) [Cp Nd(ant)] (toluene room temperature) in the region of hypersensitive {-{-transitions 3

580

600

6 2 0

'—• \ t ] nm

2

2

y


2

70


have turned out to be e q u i l i b r i u m mixtures i n v o l v i n g at l e a s t some of the d i f f e r e n t s u b s t i t u t i o n products p r i n c i p a l l y imaginable (30). Such r e s u l t s which are mainly supported by massand NMR-"spectroscopic f i n d i n g s (27) are c o n s i s t e n t with the general behaviour of f-metal c h e l a t e complexes (31), but d i f f e r from the we11-documented apparently higher complex s t a b i l i t y of the corresponding T i - and even Sc-complexes (32) . The a b s o r p t i o n spectrum of the m a t e r i a l obtained from Cp3Nd and H-diket with R = t e r t - b u t y l c l e a r l y shows that the s t a r t i n g compound has been attacked by the a c i d . The data of Table IV indicate for diket = 2,2 ,6,6 -tetramethylheptane-3,5-dionate (thd) that most fragments apparently i n v o l v e two or even three thd-moieties although Cp3Ln and H-tmd had been reacted i n e q u i molar q u a n t i t i e s . f


SPECTROSCOPY

l

Reaction with fi-Ketoimines. A d i f f e r e n t s i t u a t i o n i s met i f the B-diketone H-diket i s r e p l a c e d by a r e l a t e d B-ketoimide (or s e m i - S c h i f f base), H-ketim (33): R "H-ketim

M

=

HC^.

H

R = CH R = C H , t-C^H

(12)

3

?

6

R

5

9

R'

With t h i s modified c h e l a t e l i g a n d "ketim" (and Ln h e a v i e r than Nd) i t has been p o s s i b l e to a r r i v e at s u f f i c i e n t l y k i n e t i c a l l y s t a b l e complexes [Cp Ln(ketim) ] which t u r n out to represent the f i r s t examples of the general type Cp2Ln(chel). Contrary to the known B-diketonato-complexes Cp2M(chel) (M = Sc,. T i ) ( 3 2 ) none of the f o r m a l l y r e l a t e d Ln-systems occurs as a monomer i n s o l u t i o n . The y e l l o w complex [ C p Y b ( k e t i m ) ] with R = CGH d i s p l a y s mass-, H-NMR- and o p t i c a l s p e c t r a c o n s i s t e n t with i t s f o r m u l a t i o n as a b i s ( n - C p ) - c o m p l e x i n v o l v i n g b r i d g i n g ketim l i g a n d s (30). The corresponding complex w i t h R = t - C i t H g has so f a r been obt a i n e d as an o i l which i s d i f f i c u l t to p u r i f y . Table V d i s p l a y s the ^-NMR data of [Cp2Yb(ketim)] at v a r i o u s temperatures. The r a t h e r d i f f e r e n t i s o t r o p i c s h i f t s ( o p p o s i t e signs!) of the two methyl groups suggest t h e i r l o c a t i o n i n f a i r l y d i f f e r e n t "magnetic environments". I t i s , however, not p o s s i b l e to decide i f there are N- or 0 - b r i d g i n g l i n k s . As o n l y one Cp r i n g proton resonance appears, some f l u x i o n a l behaviour of the b r i d g i n g ketim l i g a n d i s not u n l i k e l y . Contrary to the mass s p e c t r a of the B-diket-complexes, [ C p Y b ( k e t i m ) ] (with R = C H ) gives r i s e to a spectrum i n v o l v i n g the expected fragments: M , M-Cp , M-2Cp , and M-ketim . However, no fragments i n v o l v i n g two Yb-atoms are observed. On r e a c t i o n of Cp3Yb with two moles of H-ketim, a y e l l o w product of the expected composition [ C p Y b ( k e t i m ) ] (R = C 6 H 5 ) i s obtained. S i m i l a r l y , the r e a c t i o n of Cp3Yb w i t h the p o t e n t i a l 2

n

?

!

2

2

5

1

5

f

2

2

2

6

5

+

+

+

+

1

2

R


4.

FISCHER AND BIELANG

Mixed-Ligand

Organolanthanide

Complexes

71

Table IV. Mass s p e c t r o s c o p i c data of two products C p L n ( t h d ) . ( a ) : Ln = Nd, 130 °C; ( b ) : Ln = Yb, 100 °C. M

n

2

~1 ion

m/e (a) (b) +

Ln(thd) {Ln(thd) - H } {Ln(thd) - CH } {Ln(thd) - C H } { L n ( t h d ) - t-Ci.Hg} ' Ln(thd) {Ln(thd) - C H } { L n ( t h d ) - t-C^Hg}"*" Ln(thd) {Ln(thd) - C H } (Ln(thd) - t-C^Hs}" " CpLn(thd) Cp Ln(thd) CpLn(thd) Cp Ln CpLn

-

723

689

-

-

708 681 666 540 510 482 357 326 299 -

3

+

3

2


+

3

3

+

3

3

6

4

3

+

508 478

2

+

2

2

6

-

2

+

325

-

+

2

7

1

+

573 455 390 272 207

2

+

2

+

+

2

+

r e l . intensity(%) (b) (a)

-

18,3

-

3,7

-

3,4 2,0 56,5 100,0 3,0 6,7 35,2 6,0 2,7

100,0 6,4

11,7

-

-

4,2 11,4 67,7 13,5 6,4

-

x

Table V. H-NMR-data of [Cp Yb(ketim)] (R = C H ) i n toluene-ds s o l u t i o n . I n t e r n a l standard: TMS; i n parentheses r e l a t i v e i n t e n s i t i e s . One s i g n a l of i n t e n s i t y (1) i s undetectable. 2

T/K 300 285 265 245 225 205

2

6

5

C 6H5

(10)

CH (3)

CH (3)

CH (1)

(2)

(2)

-33,91 -36,91 -42,21 -48,54 -54,50 -61,90

11,88 13,48 16,03 18,68 22,61 26,76

-11,26 -12,54 -14,63 -17,02 -19,89 -23,18

-46,07 -49,16 -54,66 -56,97 -66,30 -72,75

36,21 38,43 41,80 45,38 49,57 54,01

44,43 47,31 52,00 56, 19 61,57 67,24

C5H5

3

3


72


"double

CH

c h e l a t e " "H -acacen"

CH2-CH2 C-N

Hcf

£H

3

^N-C H ":)CH

fa

/f-O*'

CH

(34)

2

3 N

SPECTROSCOPY

= H -acacen

(13)

2

V - C CH

3

3

y i e l d s i n a c l e a n r e a c t i o n a species of the composition [CpYb ( a c a c e n ) ] . Both complexes e x h i b i t o p t i c a l s p e c t r a reminiscent of other CpYbX -systems, whereas the H-NMR-spectra t u r n out too complicated to be r e l i a b l y i n t e r p r e t e d . The complex [CpYb ( k e t i m ) ] i s a l s o obtained by r e a c t i n g [ C p Y b ( k e t i m ) ] with one f u r t h e r mole of H-ketim. S t a r t i n g from Cp LnX-systems such as [ C p Y b C l ] , novel organ o m e t a l l i c s i n v o l v i n g three d i f f e r e n t l i g a n d s are obtained, e.g. n

x


2

n

2

2

l/2[C YbCl] (red) P 2

2

2

2

+ H-ketim

2

^ o l f •> ^ Z

L

(14) [CpYb(ketim)Cl] (red-brown)

x

+

HCp

The complex [CpYb ( k e t i m ) C I ] i s n o n - v o l a t i l e and s p a r i n g l y s o l u b l e even i n THF, suggesting again an o l i g o m e r i c s t r u c t u r e l i n k e d v i a CI- and/or b r i d g i n g ketiminato groups. Such complexes i n v o l v i n g s t i l l one h a l i d e l i g a n d are expected to r e a c t with a l k a l i o r g a n i c reagents, M-R, thus o f f e r i n g a new route towards CpLn(chel)Rsystems i n v o l v i n g three d i f f e r e n t ligands per metal. Although [CpYbCl] a l s o r e a c t s r e a d i l y with B-diketones, H-diket, a l l r e a c t i o n products so f a r obtained could not be p u r i f i e d enough to c o n f i r m the formation of one s i n g l e compound. As the c e n t r a l metal Ln i s v a r i e d from the end of the l a n thanide s e r i e s towards the f i r s t h a l f , v a r i o u s complications a r i s e p a r t i c u l a r l y i n the ^-NMR-, o p t i c a l and mass s p e c t r a i n d i c a t i n g the usual r e l u c t a n c e of Ce - Nd to form r e g u l a r Cp LnX-systems. Thus the pale blue (1:1) r e a c t i o n product of H-ketim (R = C 6 H 5 ) and Cp Nd suggests by i t s s l i g h t s o l u b i l i t y even i n pentane, and i t s much lower thermal s t a b i l i t y r e l a t i v e to Cp Nd, that the Cp Nd had i n f a c t reacted with the H-ketim. However, the o p t i c a l a b s o r p t i o n spectrum of the product d i f f e r s only s l i g h t l y from the spectrum of a u t h e n t i c Cp Nd, the d i f f e r e n c e s being most pronounced i n pentane s o l u t i o n and almost non-existent f o r a s o l i d t e f l o n p e l l e t . These r e s u l t s d i f f e r from those obtained on " C p N d ( d i k e t ) " i n that a Cp Nd/Lewis base adduct seems to occur as a f i n a l product i n the former case, but apparently a mixture of Cp Nd(diket) -systems (n+m = 3) with n < 3 i n the l a t t e r . Independent support f o r the formation of a Cp Ln/Lewis base adduct ( i n s p i t e of the l i b e r a t i o n of one e q u i v a l e n t of cyclopentadiene x

2

2

3

3

3

3

2

3

n

m

3


4.

FISCHER AND BIELANG

Mixed-Ligand

Organolanthanide

Complexes

73

1

during the i n i t i a l r e a c t i o n ) i s a l s o provided by the H-NMRspectrum of a " C p P r ( k e t i m ) " - s o l u t i o n which d i s p l a y s an intense resonance t y p i c a l of Cp3Pr-systems. In Table VI the mass s p e c t r o s c o p i c behaviour of v a r i o u s r e p r e s e n t a t i v e s of the s e r i e s " C p 2 L n ( k e t i m ) " with Ln = Pr, Nd, Sm and Yb, and R = C6H5, i s summarized. I t i s immediately apparent that the tendency of the primary species to undergo subsequent rearrangements towards CpsLn decreases along with the i o n i c r a dius of L n . Our present r e s u l t s suggest that i t should be p o s s i b l e to f i n d a s u i t a b l e chelate l i g a n d (chel) that could s t a b i l i z e an intermediate of the i n t r a m o l e c u l a r l i g a n d t r a n s f e r p o s t u l a t e d f o r a dimeric C p 2 L n ( c h e l ) — s y s t e m (Figure 4 ) . Likewise, i t w i l l be a matter of an optimal choice of the secondary l i g a n d to a r r i v e at genuine Cp2LnX-systems even i f Ln = Pr or Nd. There i s some evidence from the o p t i c a l s p e c t r a that C p 3 N d and anthranilaldehyde (H-ant) give r i s e to a w e l l s o l u b l e , probably dimeric s p e c i e s , [ C p 2 N d ( a n t ) ] 2 (Figure 5 ) . U n l i k e H-diket and H-ketim, r e s p e c t i v e l y , the reagent H-ant already belongs to the group of a c i d s that are weaker than C5H6. 2


3 +

Reaction with Weak Proton A c i d s : 1-Alkynes. While pyrazole (pK < 16) i s capable of r e p l a c i n g up to three Cp-ligands from Cp Ln, p y r r o l e (pK > 16) can l i b e r a t e only one Cp-ligand. S i m i l a r observations have been made on the r e l a t e d N - h e t e r o c y c l i c systems i n d o l e and c a r b a z o l e . Although none of the i s o l a t e d complexes of the type [ C p 2 L n X ] i s l i k e l y to be mononuclear, the o p t i c a l s p e c t r a of the i n d o l y l - s y s t e m [ C p 2 Y b ( i n d o ) ] suggest, l i k e f o r Y b ( p y r ) , a h a p t i c i t y n with n between 1 and 5 (Figure 6). Very s u r p r i s i n g l y , even p r o t i c " a c i d s " as weak as various 1-alkynes, HCCR, have been found to r e a c t with Cp Ln-complexes, g i v i n g r i s e to s u b s t i t u t i o n products of the type [CpLnCCR] . So f a r , s i x d i f f e r e n t 1-alkynes w i t h the f o l l o w i n g s u b s t i t u e n t s R have been adopted (37): R = n - b u t y l , n-hexyl, c y c l o h e x y l , phenyl and f e r r o c e n y l (= F c ) . With the exception of R = c y c l o h e x y l where r e a c t i o n (15) occurs already at room temperature the optimal r e a c t i o n temperature a

3

a

n

x

n

3

3

n

Cp Yb

+ HCCR

3

->

~[Cp YbCCR] 2

x

+

CpH

(15)

i s 60 - 80 °C. Table VII summarizes some c h a r a c t e r i s t i c propert i e s of the r e s u l t i n g Yb-alkynyl complexes. A l l compounds are n o n - v o l a t i l e i n vacuo and very r e l u c t a n t to adopt a decently c r y s t a l l i z e d form. By comparison with p u b l i s h e d data, the comp l e x with R = C6H5 i s i d e n t i c a l to the complex C p 2 Y b C C C H prepared by T s u t s u i and E l y (35) from [Cp YbCl]2 and L i C H . While T s u t s u i et a l . have not been able to provide any f u r t h e r information on the nature of the homologous products C p 2 L n C C C H with Ln = Gd, Ho, E r , Yb the much b e t t e r s o l u b i l i t i e s 6

2

6

6

5

5


5

74


Table VI. Mass s p e c t r o s c o p i c data of v a r i o u s products C p L n ( a p o ) ("apo" = ketim with R = C H ) . Source temperatures between 175 °C (Yb) and 250 °C (Sm). M

M

2

6

Ln

Pr

+

446 445 381 380 305


2

+

2

+

6

+

3

+

+

LnCp LnCp LnCp Ln

+ 3 + 2

+

+

Sm

Nd

%

m/e Cp Ln(apo) {Cp Ln(apo)-H} CpLn(apo)+ {CpLn(apo)-H} {CpLn(apo)-C H } Ln(apo) {Ln(apo)-H}

5

m/e

1,5 2,4 6,5 29,5 7,6

%

m/e

Yb

%

m/e

447

14,7

-

-

-

-

-

455

43,9

478

-

-

-

-

381

80,4

390

100,0

413

100,0

R

colour

n-C Hi3

yellow orange it if

6

n-Ci^Hg

C Hn Fc C H 6

6

5

II

2

30, 1

-

-

-

-

-

-

326

69,7

-

-

-

-

348

49,0

336 271 206 141

62,7 100,0 49,1 8,2

337 272 207 142

14,7 36,3 34,3 100,0

_

-

-

-

282 217

43,2 48,5

304 239

-

-

-

Table V I I . Some c h a r a c t e r i s t i c p r o p e r t i e s of the v a r i o u s products [ C p Y b C R ] (Fc = f e r r o c e n y l ) . 2

%

n

Av(CEC) 1

(cm" ) -57 -57 -18 -54 -56

decomp. temp. (°C) 180 150 150 130 180

solubility (toluene) very good II ti good n insoluble


3,7 7,4

-


FISCHER AND BIELANG

Mixed-Ligand

Organolanthanide

Complexes

10.230 —

Figure 6. NIR/VIS-absorption spectra of (a) Cp Yb (toluene solution) and (b) of Yb(pyr) (THF-solution). Note the {-{-absorptions above 11.000 cm' which suggest ^'-coordination (n > 1) of (pyr). 3

1

3


76

LANTHANIDE AND

ACTINIDE CHEMISTRY AND

SPECTROSCOPY

p a r t i c u l a r l y of the complexes with R = n-Ci+Hg and n-CeHi3 have admitted c r y o s c o p i c molecular weight studies i n benzene according to which these systems are most probably t r i m e r i c . C a r e f u l t h i n - l a y e r chromatographic studies i n the case R = Fc have proved that no other ferrocene d e r i v a t i v e s than "Cp YbCCFc" occur. By t h i s observation a l l a l t e r n a t i v e r e a c t i o n patterns i n v o l v i n g a r e a c t i o n of the C C - t r i p l e bond can be r u l e d out, l e a v i n g a loose adduct of the type (16) 2

Hi Cp Yb«---jj

(16)

3


9 R as the most probable intermediate. While r e a c t i o n s of type (15) with acetylenes have not been described before, the observation of a very small paramagnetic s h i f t of s o l u t i o n s of Cp3Nd (Cp = C H and d^Cs^U) i n the presence of HCCC H was assigned to the corresponding adduct Cp Nd-HCCC H (36). In c o n t r a s t to these l a t t e r observations, we found that Cp3Nd r e a c t s , i n s p i t e of i t s poor s o l u b i l i t y , with a l l 1-alkynes even at room temperature. Rather s u r p r i s i n g l y , the r e s u l t i n g products are orange to red i n colour (Cp3Nd i s pale b l u e ) , and t h e i r IR-spectra are devoid of a v(CEC) v i b r a t i o n a l band i n the expected r e g i o n . Nevertheless, the o p t i c a l absorpt i o n s p e c t r a due to the f - f - t r a n s i t i o n s are again i d e n t i c a l to the corresponding spectra of authentic Cp Nd. The red c o l o u r of the new products i s , however, accounted f o r by the very extended low-energetic wing of an intense n o n - f - f - t r a n s i t i o n . Unf o r t u n a t e l y , the low s o l u b i l i t y of a l l products, even i n case of R = C 6 H i , has so f a r hampered a l l NMR-studies,and attempts to grow c r y s t a l s f o r a s t r u c t u r a l determination. 5

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x

The H-NMR-spectra of [ C p Y b C C ( n - C H i ) ] a n d i t s homologue [Cp YbCC(n-Ct+Hg)] 3 are extremely s i m i l a r (see Figure 1) and can be e a s i l y assigned i n terms of an " i n t e r n a l s h i f t reagent e f f e c t " which gives r i s e to seven and f i v e , widely spaced s i n g l e t s , r e s p e c t i v e l y , f o r the Cp r i n g protons and f o r the methylene or met h y l protons i n a- to 03-position. As the s i n g l e t i n the range c h a r a c t e r i s t i c f o r the Cp r i n g protons i s accompanied by a weaker s a t e l l i t e , the presence of another organometallic by-product i n much lower q u a n t i t i e s cannot be completely r u l e d out. Graphical p l o t s of the observed i s o t r o p i c s h i f t s versus 1/T give i n a l l cases r i s e to s e r i e s of s t r a i g h t l i n e s (Figure 2) which r e s u l t seems to be somewhat i n favour of one s i n g u l a r spec i e s r a t h e r than of e q u i l i b r i a of throughout very r a p i d l y i n t e r converting species [Cp YbCCR] with d i f f e r e n t x. A l l i s o t r o p i c s h i f t s e x h i b i t e d by the two n - a l k y l a c e t y l i d e complexes are unexpectedly l a r g e by comparison with the spectra of e.g. [CpYb0 C(n-Ci H )] and Cp Yb(n-C^Hg) P (38) . One p o s s i b l e explana2

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Mixed-Ligand

Organolanthanide

Complexes

77

t i o n f o r these f i n d i n g s i s a very "compact" s t r u c t u r a l arrangement of the oligomers that would allow the exposure of the v a r i o u s n u c l e i i n R to the magnetic f i e l d of more than one paramagnetic Yb -ions. The H-NMR s p e c t r a of the Yb-alkynyl complexes with R = CeHii and Fc support the assumption of c o n s i d e r a b l e s t e r i c cong e s t i o n . Thus the low-temperature s p e c t r a of the c y c l o h e x y l system do not r e f l e c t the expected appearance of a x i a l l y and e q u a t o r i a l l y s u b s t i t u t e d cyclohexane (37). For the time being, the best model system to exemplify the p a r t i c u l a r type of a l k y n y l b r i d g i n g may be the aluminium compound (CH3)2AIC2CH3 which i s dimeric both i n the c r y s t a l l i n e and i n the gaseous state (39). The Av(C=C)-values known f o r t h i s main group metal a l k y n y l system match n i c e l y those l i s t e d i n Table V I I . 3 +


1

Reaction with other weakly CH-acidic compounds. Organic proton a c i d s of an a c i d i t y intermediate between cyclopentadiene and 1-alkynes are represented by v a r i o u s d e r i v a t i v e s of c y c l o pentadiene. We have found that e.g. indene and fluorene do not r e a c t with C p 3 Y b i n b o i l i n g toluene, but during the c a r e f u l evap o r a t i o n of the s o l v e n t , as w e l l as under s o l v e n t - f r e e c o n d i t i o n s , a r e a c t i o n takes p l a c e , y i e l d i n g brownish-yellow products of very weak s o l u b i l i t y even i n THF (27). The composition [Cp2YbL] (L = i n d e n y l or f l u o r e n y l ) i s suggested by the elemental analyses. In view of the f a c t that a monomeric t r i s ( r | - i n d e n y l ) complex of Yb of green c o l o u r i s known (40). the brownish-yellow products might be oligomers i n which the l i g a n d L p l a y s a s i m i l a r r o l e as i n the dimeric methyl complex, [Cp2Yb(1J-CH3)] 2 (41). In a very s i m i l a r manner, N,N-dimethyl-o-toluidine r e a c t s with Cp Yb to give a very unstable green l : l - a d d u c t . A f t e r r e f l u x i n g the toluene s o l u t i o n f o r ca. one hour, i t s c o l o u r turns orange-brown, and again a very p o o r l y s o l u b l e brown powder i s f i n a l l y i s o l a t e d . In view of the c o n s i d e r a b l e i n s t a b i l i t y of many Cp Ln/Lewis base adducts i t i s worth n o t i n g that i n the absence of any p o t e n t i a l l y a c i d i c C-H bond i n t a c t adducts even with r a t h e r unusual Lewis bases such as d-metal carbonyls and metal carbonyl anions, r e s p e c t i v e l y , can be i s o l a t e d (42). x

5

3

3

Acknow1e d gement s We are g r e a t l y indebted to the Deutsche Forschungsgemeins c h a f t , Bad Godesberg, and the Fonds der Chemischen I n d u s t r i e , F r a n k f u r t (Main), f o r f i n a n c i a l support. We a l s o thank B. Kanellakopulos (Karlsruhe) and T.J. Marks (Evanston) f o r s t i m u l a t i n g discussions.


78



Literature Cited 1. Marks, T.J.; Progr. Inorg. Chem., 1978, 23, 51. 2. Marks, T.J.; Fischer, R . D . , Eds. "Organometallics of the f-Elements"; D. Reidel Publ. Comp., Dordrecht, Boston, London, 1979. 3. Schumann, H . , Nachr. Chem. Tech. Lab., 1979, 27, 393. 4. Schumann, H . ; Müller, J., Angew. Chem., 1978, 90, 307. 5. Schumann, H . ; Hohmann, S., Chem. Z t g . , 1976, 100, 336. 6. Mazzei, A . , loc. c i t . Ref. 2, p. 379. 7. According to references quoted in Ref. 1, p. 99. 8. Poggio, S.; Brunelli, M . ; Pedretti, U . ; L u g l i , G . ; communicated on the N.A.T.O.-ASI on "Organometallics of the f-Elements", Sogesta, Urbino (Italy), Sept. 11-22, 1978. 9. Fischer, R.D.; Landgraf, G . , unpublished results (1975). 10. Fischer, H . , Dissertation, Technische Universität München, 1965; Fischer, E . O . ; Fischer, H . , J. Organometal. Chem., 1966, 6, 141. 11. Marks, T.J.; Grynkewich, G.W., Inorg. Chem., 1976, 15, 1302. 12. Kanellakopulos, B . ; Dornberger, E.; Billich, H . , J. Organometal. Chem., 1974, 76, C42. 13. Fischer, R.D.; Klähne, E.; Kopf, J., Z. Naturforsch., 1978, 33b, 1393. 14. Dornberger, E.; Klenze, R.; Kanellakopulos, B . , Inorg. Nucl. Chem. L e t t . , 1978, 14, 319. 15. Jamerson, J . D . ; Takats, J., J . Organometal. Chem., 1974, 78, C23. 16. Bielang, G . ; Fischer, R . D . , J. Organometal. Chem., 1978, 161, 335. 17. Schumann, H . , personal communication. 18. Bagnall, K.W.; Tempest, A . C . , loc. c i t . Ref. 2, p. 233. 19. Maginn, R . E . ; Manastyrskyj, S.; Dubeck, M . , J. Amer. Chem. Soc., 1963, 85, 672. 20. Kanellakopulos, B . , Habilitation Thesis, Universität Heidelberg, 1972; loc. c i t . Ref. 2, p. 24 (Fig. 5.12). 21. Schlosser, M . , "Struktur und Reaktivität polarer Organometalle", Springer-Verlag Berlin, Heidelberg, New York, 1973, p. 43. 22. Tsutsui, M . ; unpublished observations (1965) cited in Gysling, H . ; Tsutsui, M., Adv. Organometal. Chem., 1970, 9, 365. 23. Pappalardo, R.; Jørgensen, C . K . , J. Chem. Phys., 1967, 46, 632. 24. Fischer, R.D. in "NMR of Paramagnetic Molecules", LaMar, G.N.; Horrocks, W. DeW.; Holm, R . H . , Eds., Academic Press, New York and London, 1973, p. 521. 25. Fischer, R.D., loc. c i t . Ref. 2, p. 337. 26. Marks, T.J.; Seyam, A.M.; Kolb, J . R . , J. Amer. Chem. S o c ., 1973, 95, 5529. 27. Bielang, G . , Dissertation, Universität Hamburg, 1979.



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Mixed-Ligand

Organolanthanide Complexes

28. Agarwal, S.K.; Tandon, J.P., Monatsh. Chem., (1979), 110, 401. 29. The ytterbium complex was also independently prepared by E. Mastoroudi and B. Kanellakopulos; personal communication. 30. Bielang, G . ; Fischer, R . D . , Inorg. Chim. Acta, 1979, 36, L 389. 31. Bagnall, K.W., loc. c i t . Ref. 2, p. 231; Siddall III, T . ; Stewart, W.E., J. Chem. Soc. Chem. Communic., 1969, p. 922. 32. Coutts, R . S . P . ; Wailes, P . C . , J. Organometal. Chem., 1970, 25, 117; Austr. J . Chem., 1969, 22, 1547. 33. Combes, M.A., B u l l . Soc. Chim. France, 1888, [2], 49, 89; Holtzclaw, Jr., H . F . ; Collman, J.P.; A l i r e , R.M., J. Amer. Chem. S o c ., 1958, 80, 1100. 34. McCarthy, P.J.; Hovey, R.J.; Uena, K . ; Martell, A.E., J . Amer. Chem. S o c ., 1955, 77, 5820. 35. Tsutsui, M . ; E l y , N.M., J . Amer. Chem. S o c ., 1975, 97, 1280 and 3551; Inorg. Chem., 1975, 14, 2680. 36. Crease, A . E . ; Legzdins, P . , J . Chem. Soc. Dalton Trans., 1973, 1501. 37. Fischer, R.D.; Bielang, G . , J. Organometal. Chem., in press. 38. Marks, T.J.; Porter, R.; Kristoff, J . S . ; Shriver, D . F . , in "Nuclear Magnetic Resonance Shift Reagents" Academic Press, New York, 1973, p. 247. 39. Fries, W.; Schwarz, W.; Hausen, H . - D . ; Weidlein, J.; J. Organometal. Chem., 1978, 159, 373, and further references therein. 40. Tsutsui, M . ; Gysling, H.J., J. Amer. Chem. Soc.. 1968. 90, 6880; i b i d . , 1969, 91, 3175. 41. Holton, J.; Lappert, M . F . ; Ballard, D.G.H.; Pearce, R.; Atwood, J.L.; Hunter, W.E., J. Chem. Soc. Chem. Communic., 1976, 480. 42. Onaka, S.; Furuichi, N . , J. Organometal. Chem., 1979, 173, 77. RECEIVED January 30, 1980.


Lanthanide and Actinide Chemistry and Spectroscopy - American

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