A simple way of recycling of homogeneous catalyst in Suzuki reaction

Figures & data

Figure 1.  Structures of the homogeneous catalysts 1 (Pd-100), 2 (Pd-106) and 3 (Pd-118).

short-legendScheme 1. Suzuki coupling of phenylboronic acid and aromatic carboxylic acid.

Table 1. Recycling of homogeneous catalyst in Suzuki reaction with basic work up (Scheme 1).

Entry	Comp No	R1	X	Y	Cycle	Catalyst (5 mol%)	% Conv (time in h)^a	% Yield/purity by HPLC
1	9a	H	COOH	H	1	Pd-100	94.3 (4)	85/97.0
2	9a	H	COOH	H	2	–	96.0 (4)	82/98.2
3	9a	H	COOH	H	3	–	94.5 (3)	70/99.0
4	9b	F	COOH	H	1	Pd-100	94.5 (3)	77/95.0
5	9b	F	COOH	H	2	–	96.0 (3)	76/96.9
6	9b	F	COOH	H	3	–	75.6 (3)	65/96.5
7	9c	OMe	COOH	H	1	Pd-100	93 (2)	81/97.9
8	9c	OMe	COOH	H	2	–	96.0 (17)	80/98.2
9	9c	OMe	COOH	H	3	–	93.3 (10)	80/94.3
10	9a	H	COOH	H	1	Pd-106	82.2 (3)	*
11	9a	H	COOH	H	2	–	93.2 (3)	*
12	9a	H	COOH	H	3	–	88.2 (3)	*
13	9b	F	COOH	H	1	Pd-106	97.0 (3)	*
14	9b	F	COOH	H	2	–	97.7 (3)	*
15	9b	F	COOH	H	3	–	96.6 (3)	*
16	9c	OMe	COOH	H	1	Pd-106	93.2 (3)	*
17	9c	OMe	COOH	H	2	–	89.2 (3)	*
18	9c	OMe	COOH	H	3	–	95.5 (3)	*
19	9a	H	COOH	H	1	Pd-118	96.2 (3)	*
20	9a	H	COOH	H	2	–	91.8 (3)	*
21	9a	H	COOH	H	3	–	94.7 (3)	*
22	9b	F	COOH	H	1	Pd-118	96.8 (3)	*
23	9b	F	COOH	H	2	–	97.1 (3)	*
24	9b	F	COOH	H	3	–	97.1 (3)	*
25	9c	OMe	COOH	H	1	Pd-118	95.4 (3)	*
26	9c	OMe	COOH	H	2	–	96.3 (3)	*
27	9c	OMe	COOH	H	3	–	96.9 (3)	*
28	9d	H	H	COOH	1	Pd-118	94.5 (3)	*
29	9d	H	H	COOH	2	–	94.6 (3)	*
30	9d	H	H	COOH	3	–	93.3 (4)	*
^a% Conversion to product, with respect to starting material; *Product was not isolated.

short-legendScheme 2. Suzuki coupling of phenylboronic acid and aromatic amine.

Table 2. Recycling of homogeneous catalyst in Suzuki reaction with acidic work up (Scheme 2)

Entry	Product	X	R1	Cycle	Catalyst (5 mol%)	% Conv (time in h)^a
1	12a	H	F	1	Pd-118	98 (1)
2	12a	H	F	2	–	98 (1)
3	12a	H	F	3	–	92 (1)
4	12a	H	F	1	Pd-100	85 (2)
5	12a	H	F	2	–	72 (4)
6	12a	H	F	3	–	57 (4)
7	12b	N	F	1	Pd-118	90 (4)
8	12b	N	F	2	–	88 (5)
9	12b	N	F	3	–	72 (5)
10	12b	N	F	1	Pd-100	71 (24)
11	12b	N	F	2	–	53 (24)
12	12b	N	F	3	–	27 (24)
^a% Conversion to product, with respect to starting material.

Figure 1.  ¹H NMR spectra of compound 9a.

Figure 2.  ¹³C NMR spectra of compound 9a.

Figure 3.  HPLC for compound 9a.

Figure 4.  ¹H NMR spectra of compound 9b (Note: peak at 1.18 (t), 1.92 (s), and 4.03 (q) ppm corresponds to residual ethylacetate).

Figure 5.  ¹³C NMR spectrum of compound 9b (Note: peak at 14.0, 20.7, and 170.3 ppm are corresponds to residual ethylacetate).

Figure 6.  HPLC for compound 9b.

Figure 7.  ¹H NMR spectra of compound 9c.

Figure 8.  ¹³C NMR spectra of compound 9c.

Figure 9.  HPLC for compound 9c.

Palladium recovery/leaching of the catalyst 1 (Pd-100) in the synthesis of compound 9a

	% Pd recovery in org. layer	% Pd recovery in aq. layer
Pre-reaction condition^a	77.8	NA
First cycle	77.3	15.7
Second cycle	77.2^b	20.8
Third cycle	69.1^c	21.6
^aAnalysis was performed for the organic layer before subjected to reaction.
^bCalculation was done based on the first cycle catalyst input.
^cCalculation was done based on the second cycle catalyst input.